Mountain height word problem
Using some basic algebra to solve what looks like a hairy word problem that involves proportions.
Discussion and questions for this video
 Let's start with a warm up ratio problem.
 Then we can tackle some harder word problems. So I have the
 ratio 13/6 is equal to 5/x.
 I don't like having this x in the denominator, so let's
 multiply both sides of this equation by x.
 So if I multiply both sides by x, what's going to happen?
 On the right hand side, this x cancels out with that x.
 And then the left hand side going to become 13 over 6x is
 equal to you're just going to have a 5 there.
 And then to solve for x, you just multiply both sides by
 the inverse of 13/6.
 6/13.
 These, obviously, cancel out.
 That's why I multiplied it by the inverse.
 And you get x is equal to 5 times 6, which is 30/13.
 Now one way that you might see this done it's kind of
 skipping a step is called cross multiplying.
 You look at a ratio like this, and you immediately say the
 numerator on this side times the denominator on that side
 is equal to the numerator on this side times the
 denominator on that side.
 Let me write that out.
 So you might sometimes see people immediately go to let
 me just rewrite the problem actually So that original
 problem was 13/6 is equal to 5/x.
 You might sometimes immediately see someone go to
 13 times x is equal to 5 times 6.
 And it might look like magic.
 How does that work out?
 Why does that make sense?
 And really, all they're doing to get to this point is they
 are simultaneously multiplying both sides of the equation by
 both denominators.
 Let me show you what I mean.
 If I multiply both sides of this equation by 6 and an x,
 what's going to happen?
 If I multiply it by 6x times both sides of this equation
 And where did I get the 6?
 From here.
 Where did I get the x?
 From there.
 Both denominators.
 What's going to happen?
 On this side of the equation, the 6 is going to cancel out
 with this denominator.
 And on the right hand side of the equation, the x is going
 to cancel with this denominator.
 So you're going to be left with 13 times x is
 equal to 5 times 6.
 So nothing fancy there.
 You're just multiplying by the denominators of both sides of
 the equation.
 And it looks like you're cross multiplying.
 13x is equal to 5 times 6.
 And then from here, of course, you divide both sides by 13.
 You get x is equal to 30/13.
 Now that we're all warmed up, let's tackle some actual word
 problems.
 So we have the highest mountain in
 Canada is Mount Yukon.
 It is 298/67 the size of then Ben Nevis.
 Let's Y for Yukon is equal to 298/67 the size of let's say
 N for Nevis.
 That's what this in green tells us.
 The highest peak in Scotland.
 Mount Elbert in Colorado is the highest peak
 in the Rocky Mountains.
 Mount Elbert so we have this other information here Mount
 Elbert is 220/67 the height of Ben Nevis.
 So let's say, E for Elbert.
 E is equal to 22/67 times Nevis.
 Times the same Ben Nevis, right there.
 And they're telling us more.
 And, it is 44/48 the size of Mont Blanc.
 So Elbert is equal to 44/48 the size of Mont Blanc.
 Let's write B for Mount Blanc.
 They also tell us Mont Blanc is 4,800 meters high.
 Mont Blanc is 4,800.
 meters high.
 So B is equal to 4,800.
 And they ask us, how high is Mount Yukon?
 So we have to figure out Y.
 So let's see if we can work backwards, and figure out all
 the variables in between.
 So let's start with this information here.
 B is equal to 4,800.
 E is equal to 44/48 times B.
 So E so Elbert is equal to 44/48 times Mont Blanc, which
 is 4,800 meters.
 Now if you divide that by 48 4,800 divided by 48 is 100.
 So Elbert is 44 times 100 meters high.
 So it's equal to 4,400 meters.
 Fair enough.
 Now we can use this information and
 substitute it over here.
 We get Elbert, which is 4,400 meters high, is equal to
 220/67 times Ben Nevis.
 N for Nevis.
 To solve for Nevis, we multiply both sides by the
 inverse of this coefficient right here.
 So we multiply both sides by 67/220.
 So times 67/220.
 The 67 cancels with that 67.
 That 220 cancels with that 220.
 And then you get let's see, if I take 4,400 divided by
 220 440 divided by 220 is 2.
 So this is going to be 20.
 So 4,400 divided by 220 is just 20.
 So you get Nevis is equal to I'll swap sides.
 So Ben Nevis is equal to 67 times 20 meters.
 And now that's what?
 1,340 meters.
 Is that is right?
 Well, lets just leave it like that, because we could
 actually it looks like that's 67 I'm going to leave Nevis
 as 67 times 20 meters.
 And substitute it right there.
 So Yukon I'll just go down here, because I have more real
 estate there Yukon is equal to 298 over 67 times the
 height of Nevis.
 Nevis is 67 times 20.
 So times 67 times 20.
 Well I can divide 67 by 67, and I get Yukon is
 298 times 20 meters.
 So Yukon is equal to 298 times 20.
 And what is that equal to?
 That is equal to Let's see that's 2 times 298
 is going to be 396.
 Oh sorry, it's going to be 596.
 This is almost 300, so it should be close to 600.
 This is 2 less than 300, so this should
 be 4 less than 300.
 And then, I have a 0 here.
 So it's going to be 5,960 meters.
 And we are done.
 Let's do one more of these word problems. All right.
 At a large high school, it is estimated that 2 out of every
 3 students have a cell phone.
 And 1 in 5 of all students have a cellphone that is one
 year old or less.
 All right.
 So let's think about it.
 Let's say that x is equal to the total number of students.
 This first line, 2 out of 3 students have a cell phone, so
 we could say that 2/3 x have cell phone.
 That's what that green statement tells us.
 And then that purple statement 1 in 5 of all
 students have a cellphone that is one year old or less.
 So 1/5 x have less than 1/5 year cell phone.
 So they want to know, out of the students who own a cell
 phone so it's out of this that's our denominator.
 So let me write that down.
 That is our denominator.
 So out of the students who have a cellphone that's
 right there they want to know what proportion owns a
 phone that is more than one year old.
 So how many students have a cell phone that is more than
 one year old?
 Well, we could take the total number that have a cellphone,
 which is 2/3 x.
 2/3 of all the students have a cell phone.
 We can subtract out all of the students that have a new
 cellphone a cell phone that is less than one year.
 Remember they're saying more than one year here.
 So we want to subtract out all the students with the new
 cellphone, minus 1/5x, and you will then have the proportion
 of students who have this right here.
 This is right here.
 This is, have greater than 1/5 year cell phone.
 They have a phone, but it's more than 1/5 years old.
 This is all of them that have a cellphone.
 We subtract out the new ones.
 So this is, essentially, all of the people who have an
 older than oneyear old cell phone.
 So to solve this, we just subtract the fractions.
 So this is just going to be, let's see, 2/3 is the same
 thing as 10/15.
 That's 2/3 minus 1/5.
 The same thing as 3/15 x.
 Which is equal to 10 minus 3 is 7/15 x.
 Is the total proportion of students that's this
 orange what proportion owns a phone that is more
 than one year old?
 It's 7/15 x.
 That's an actual number.
 So if you want to know, out of the students who own a cell
 phone so out of the students who own a cell phone, right
 there 2/3x, what proportion owns a phone that it is more
 than one year old?
 This is the number that own a cellphone that is more than
 one year old.
 And this whole value is the proportion out of the students
 who have a cell phone.
 Lucky for us, the x's cancel out.
 And we are left with this is equal to 7/15 times the
 inverse of the denominator.
 You divide by 2/3.
 That's the same thing as multiplying by 3/2.
 And what does this equal to?
 Divide by 3.
 We are left with 7/10.
 So of the students who own a cell phone, 7 out of 10 of the
 students who own a cell phone, own a cell phone that is more
 than one year old.
 And we are done.
Be specific, and indicate a time in the video:
At 5:31, how is the moon large enough to block the sun? Isn't the sun way larger?

Have something that's not a question about this content? 
This discussion area is not meant for answering homework questions.
in 7:44,i dont understnd the '1/5x have <1/5 yr cellphone.
That's because Sal made an error at 7:40 into the video. Sal says and writes, "One fifth x have less than one fifth year cell phone" when the problem states, "one in five of all students have a cell phone that is one year old or less." To be correct, Sal should have written "1/5 x have < 1 yr cell phone." Hope this helps. Good Luck.
no your not idiot just ask for help dont let yourself down you just need a little help with math
Guys! Whether Sal messed up or not he still tries his hardest and takes out a lot of time to make these videos. Appreciate them! Plus, he doesn't mess up a lot.
cuz he messed up. its 1 year
he was trying to write an arrow the the > is an arrow (i could be wrong tho so just double check)
Ok thanks! I'm an idiot but whatever!
Sal messed up, which is probably why. He messed up when writing his answer thing
listen. Watch the video until you understand. That is what I do. It helps a lot.
In a nutshell, can some one please explain exactly what a proportion and ratio is? (In the simplest but most knowledgeable way please)
Ratio: The quotient of two quantities that are in the same unit.
Proportion: An equation stating that two ratios are equivalent.
:) (Hope this was Helpful!) (;
Proportion: An equation stating that two ratios are equivalent.
:) (Hope this was Helpful!) (;
ratio and proportions are in a nutshell  if you get 1 almond in a bag for every 2 walnuts in the same bag it means you have 2 walnuts and 1 almond well if you get 2 almonds then by that standard you should have 4 walnuts. it can be written as 1 almond : 2 walnuts or 1 almond / 2 walnuts the ratio will always be in equal proportions so if you increase the top to a 2 almonds / x walnuts you have to increase the bottom by the same amount so 2 almonds / 4 walnuts.
the way to test if the problem is = or in proportion is to cross multiply so 1/2 = 2/4 you multiply the numerator on the one side by the denominator on the other so 1 x 4 = 4 and 2 x 2 = 4 so since both numbers come to 4 they are in proportion. hope this helps.
the way to test if the problem is = or in proportion is to cross multiply so 1/2 = 2/4 you multiply the numerator on the one side by the denominator on the other so 1 x 4 = 4 and 2 x 2 = 4 so since both numbers come to 4 they are in proportion. hope this helps.
A ratio is L compared to M.
A Proportion is saying the ratio between L and M is the same as the ratio between C and W
Example
3:9....................................................states that 3 and 9 have a relationship
9 : 27 ...................................................Same thing, 9 and 27 have a relationship
1:3::3:9::9::27..................................Says 1 and 3 have the same relationship as 3 and 9, also as 9 and 27. (A colon between them means you are stating them as a ratio. Two colon mean that you are setting them, (or that they are) related to each other in the same way.
Example of an Algebraic proportional problem
3:5::X:Y Set a new proportion where Y is 4.5 times what it is now.
Answer 3 :22.5::X:Y
Hope I didn't confuse you and helped.
A Proportion is saying the ratio between L and M is the same as the ratio between C and W
Example
3:9....................................................states that 3 and 9 have a relationship
9 : 27 ...................................................Same thing, 9 and 27 have a relationship
1:3::3:9::9::27..................................Says 1 and 3 have the same relationship as 3 and 9, also as 9 and 27. (A colon between them means you are stating them as a ratio. Two colon mean that you are setting them, (or that they are) related to each other in the same way.
Example of an Algebraic proportional problem
3:5::X:Y Set a new proportion where Y is 4.5 times what it is now.
Answer 3 :22.5::X:Y
Hope I didn't confuse you and helped.
A ratio and proportion is nothing more than _a part of a whole divided by a whole_. To get into a little better explination, think of a sport's season. Even if you don't like sports, if you are needing to know how many games a team won that year compared to how many they lost, a ratio of _how many games won_ divided by _how many game total_, should be able to tell you whether or not you should be betting your money on that team.
A proportion is saying that two _ratios_ are the same. For example, 1/2 = 2/4 is a true proportion because if you multiply *both* the numorator and the denominator of 1/2 by 2, you get 2/4, which, when reduced, is 1/2. Hope this helps(:
A proportion is saying that two _ratios_ are the same. For example, 1/2 = 2/4 is a true proportion because if you multiply *both* the numorator and the denominator of 1/2 by 2, you get 2/4, which, when reduced, is 1/2. Hope this helps(:
```
*Ratio* : _The quotient of two quantities that are in the same unit_.
*Proportion* : _An equation stating that two ratios are equivalent_.
``` hope this helps
*Ratio* : _The quotient of two quantities that are in the same unit_.
*Proportion* : _An equation stating that two ratios are equivalent_.
``` hope this helps
What are ratios and what do we use them for?
(This was my question when I was younger, I asked this question because I still haven't seen anyone ask this and I want to share my answer to those who are also curious)
(This was my question when I was younger, I asked this question because I still haven't seen anyone ask this and I want to share my answer to those who are also curious)
Ratio means (or is defined as) the quotient of two numbers or quantities indicating their relative sizes.
The ratio of a to b is written as a:b or a/b. The first term a is called the antecedent, and the second term b is called the consequent
Ratios are used when there appears a need or utility to compare numbers of quantities with one another
Whenever there's a need to do comparisons numerically, we use ratios and proportions.
For example (I'll give you 3 examples):
a) We compare Frank's age with Bob's age. Frank is 24 years old, while Bob is 12 years old. Therefore we say that the ratio of Frank's age relative to Bob's, is the ratio 2:1 (we read that as : ratio two is to one) OR that proportionately,Frank is twice Bob's age.
b) When we learn in baking that for Aunt Linda's strawberry chiffon cake we would require 4 eggs for every 2 cups of flour, while for Grandma's recipe for butter and walnut cookies we would need 1 egg for every 2 cups of flour, then we could say that (comparing the number of eggs required for the cake in comparison with the number of eggs required to bake the cookies):
the ratio of eggs required for the cake relative to the cookies is 4:1 (four is to one) or that, in order to bake the strawberry chiffon cake properly we need 4 times the number of eggs required to bake the butter and walnut cookies,or 4/1.
c) Comparing the number of years two comets(Comet Klemola and Comet Encke) take orbiting the Sun, if the Comet Klemola orbits the Sun every 11 years while the Comet Encke takes 3 years (not the exact number, you would have to compute the exact period using its precise speed, but for purposes of illustration, let's just say 3 for convenience), then the ratio of the inner cloud orbit (the astronomical term for "orbiting around the Sun") of the Comet Klemola relative to Comet Encke is 11:3 or 11/3.
Ratios are used in obsevation of quantities as well as deriving and formulating quantities. Some of the interesting applications in both Physics and Chemistry are as follows:
1.) Creating new types of alloys, after comparing relative strengths of metals and their other properties
2.) Combining chemicals to form personal care products,after comparing the speed of the effects of various components on the skin (It's not as bad as it sounds...we're talking about adding oatmeal or Vitamin E to soaps and shampoos)
3.) Cooking and baking, after much expereimentation and comparison, to make for instance, a softer, more moist red velvet cake
4.) Probability and statistics (It gets interesting after you've compared your chances for accomplishing many things, given a specific time frame)
etc........
The ratio of a to b is written as a:b or a/b. The first term a is called the antecedent, and the second term b is called the consequent
Ratios are used when there appears a need or utility to compare numbers of quantities with one another
Whenever there's a need to do comparisons numerically, we use ratios and proportions.
For example (I'll give you 3 examples):
a) We compare Frank's age with Bob's age. Frank is 24 years old, while Bob is 12 years old. Therefore we say that the ratio of Frank's age relative to Bob's, is the ratio 2:1 (we read that as : ratio two is to one) OR that proportionately,Frank is twice Bob's age.
b) When we learn in baking that for Aunt Linda's strawberry chiffon cake we would require 4 eggs for every 2 cups of flour, while for Grandma's recipe for butter and walnut cookies we would need 1 egg for every 2 cups of flour, then we could say that (comparing the number of eggs required for the cake in comparison with the number of eggs required to bake the cookies):
the ratio of eggs required for the cake relative to the cookies is 4:1 (four is to one) or that, in order to bake the strawberry chiffon cake properly we need 4 times the number of eggs required to bake the butter and walnut cookies,or 4/1.
c) Comparing the number of years two comets(Comet Klemola and Comet Encke) take orbiting the Sun, if the Comet Klemola orbits the Sun every 11 years while the Comet Encke takes 3 years (not the exact number, you would have to compute the exact period using its precise speed, but for purposes of illustration, let's just say 3 for convenience), then the ratio of the inner cloud orbit (the astronomical term for "orbiting around the Sun") of the Comet Klemola relative to Comet Encke is 11:3 or 11/3.
Ratios are used in obsevation of quantities as well as deriving and formulating quantities. Some of the interesting applications in both Physics and Chemistry are as follows:
1.) Creating new types of alloys, after comparing relative strengths of metals and their other properties
2.) Combining chemicals to form personal care products,after comparing the speed of the effects of various components on the skin (It's not as bad as it sounds...we're talking about adding oatmeal or Vitamin E to soaps and shampoos)
3.) Cooking and baking, after much expereimentation and comparison, to make for instance, a softer, more moist red velvet cake
4.) Probability and statistics (It gets interesting after you've compared your chances for accomplishing many things, given a specific time frame)
etc........
ratio is simialar to fratcions but not completly
I get it its pretty easy once you get the hang of it but sometimes when you have fractions you have to cross multiply
Yes, a ratio is similar to fractions I think you can even write a ratio as a fraction!
For example: 3:5
3/5 (3 over 5)
For example: 3:5
3/5 (3 over 5)
Meh I think it is easy
how do iu do this
MOST IMPORTANTLY: Sal wants us to get why cross multiplying works! It's just looking under the hood of the engine. Don't worry cross multiplying is the engine, it will always work! Cheers!
You Khan do it.
Just don't let the equations sit there all lonely. It's hard to go straight up you'll never convince a 2 on the bottom of 1/2 to climb over that roof. But diagnolly, any number can climb steps, even I can (and I weigh 220 lol). So Bring the lonely numbers from the bottom, to the tops diagnoly across, through the '=' elevator. Just make sure you do it to both numbers, or you end up with a very angry left out number, that will snitch on your teacher to get you marked wrong on the test!
A portion is when you give food out depending on who is there by the table. A Proportion is a professional version of that, where you give out numbers from one equation to the other equation, making sure to depend on the rules of math, you don't want one of your equation guests getting all 'undefined' on you!
Just pay attention to the video. Over time, you will most definetly understand.
You have to divide the number 639 in three parts x, y, z in order that x:z = 5:6 and y:z = 8:9 ? how can i solve this problem?
It includes a lot of algebra, so it might be a bit complicated.
639= a*b*c (I just switched the letters, it makes it more convenient)
a= (5/6)c
b= (8/9)c
639= (40/54)c^3
862.62=c^3
9.51944..=c
7.93286924..=a
8.4617..=b
To answer your original question
x= 7.9328..
y=8.4617..
z=9.5194..
x*y*z equals your number (639).
639= a*b*c (I just switched the letters, it makes it more convenient)
a= (5/6)c
b= (8/9)c
639= (40/54)c^3
862.62=c^3
9.51944..=c
7.93286924..=a
8.4617..=b
To answer your original question
x= 7.9328..
y=8.4617..
z=9.5194..
x*y*z equals your number (639).
Thanks a lot =)
Please help! I want to prepare for next year in 6th grade. I hear you study this too. Can you help explain it for me?
The last word problem is frying my brain. If x = total number of students, why would you multiply the total number of students by 1/5, because the 1/5 only applies to those who have phones which is 2/3's of x.
I was thinking how to take 1/5 out of 2/3 and come up with this. If you divide 1/5 by 2/3 (multiply the reciprical) you get 3/10 < number of students with new phones. Out of 10 students 3 have a new phone. So 7/10th have old phones or 7 out of 10. Is this another way of figuring out this problem? Sorry if this confuses anyone, I am very confused and I need to understand this. Thank you for lessons I need to watch more obviously.
I was thinking how to take 1/5 out of 2/3 and come up with this. If you divide 1/5 by 2/3 (multiply the reciprical) you get 3/10 < number of students with new phones. Out of 10 students 3 have a new phone. So 7/10th have old phones or 7 out of 10. Is this another way of figuring out this problem? Sorry if this confuses anyone, I am very confused and I need to understand this. Thank you for lessons I need to watch more obviously.
I think you misunderstood the problem. It says 1/5 out of ALL students, not 1/5 out of students that have a phone.
Sal, please help with this question:
The ratio of Science and Arts students in a college is 4:3.If 14 Science students shift to Arts then the ratio becomes 1:1.Find the total strength of Science and Arts students.
How would you solve something like this?
The ratio of Science and Arts students in a college is 4:3.If 14 Science students shift to Arts then the ratio becomes 1:1.Find the total strength of Science and Arts students.
How would you solve something like this?
3/4
3 art students for every 4 sci students
3 art students for every 4 sci students
There are 112 sci students and 84 art students.
Hope that helped! plz vote up!
Hope that helped! plz vote up!
How does this all work out
Proportions are direct comparisons between two numbers.
They are only expressed using fractions.
They are only expressed using fractions.
I don't really know, I just started at Khan Academy. Hope it helps!
At the very beginning, the first problem, I watched this part about 10 times. I still don't understand what you ares saying. My teacher said to use this website and I love it but some things are still really hard. Especially the proportions. Thank you.
Can someone please help me to understand what he did at 4:19? I understand that 4800 can be divided by 48 100 times but how is it possible to eliminate these two numbers simply because of this relationship?
Crossing these numbers out just means that he's doing the division there. Now that he's done, he doesn't need the numbers 48 or 4800, all he needs for the next step is the numerator of that fraction and the result of the other operation (100).
Not really a question but,
Thanks you Sal for being such a lifesaver! Now I understand math!
Thanks you Sal for being such a lifesaver! Now I understand math!
Yeah, I just found out today. XD
LOL you know there is a comment section at the top below the video right? XD
Help please!! I don't understand how and why Sal is dividing 44/48 by 4800, when does this rule/option apply and why can that be multiplied by 44. Thank you!!
What is the difference between ratio and proportion....... It's really getting me confused! Some please help........ Thanks :)
A ratio is a comparison between two equivalent numbers. A proportion is two ratios that are equal. And yes, they are very similar because they are both comparing numbers.
They are very similar ideas. Both are comparisons of numbers.
examples: The ratio of students to teachers is 18 to 1.
The proportion of boys in the class is 6 out of 10.
I suppose more often proportion is used to compare something to the total, but mathematically they are the same.
examples: The ratio of students to teachers is 18 to 1.
The proportion of boys in the class is 6 out of 10.
I suppose more often proportion is used to compare something to the total, but mathematically they are the same.
why did sal reverse the fraction 13/6 into 6/13 @ at the beginning??
thnkss
When you multiply a fraction by itself, you have to multiply the original by the inverse, which is just the fraction flip upside down.
Make sense?
Make sense?
In problem 2 starting at 6:53 I still a little confused when divideing the different
varibles can someone please explain?
Thank You
varibles can someone please explain?
Thank You
how do you determine whether a pair of ratios form a proportion?
So all you need to do is cross multiply and thats how you do ratio?? I really dont get it that much. I will just do prctice on it and see what I can pull together on the video. Jklolfmao19,check me out on Call of Duty Modern Warfare 3 [MW3] for PS3 and Call of Duty Black Ops 2 for Xbox 360...BEACH!!
I need help...
I don't know whether to simplify the fractions and what should multiply fractions by (x).
example:
((x) x 13/6 = 5/(x) x (x))
Real Problem:
3/9 = y/21
I don't know whether to simplify the fractions and what should multiply fractions by (x).
example:
((x) x 13/6 = 5/(x) x (x))
Real Problem:
3/9 = y/21
In this situation, I would simplify the fractions and then cancel them out.
3/9=y/21 can simplify to 1/9=y/7
then you can multiply the demoninators together and get the answer.
3/9=y/21 can simplify to 1/9=y/7
then you can multiply the demoninators together and get the answer.
At 6:36 Sal says it should be 4 less than 300. shouldn't it be 4 less than 600?
Yes, he made a mistake in what he said, but what he wrote was still correct.
There are 1,312 Students in a middle school. On any given day there may be 65 students missing. What is the percentage of students missing on any given day?
Is this the correct way to solve a problem like this?
65/1312 = x/100
1312x = 65(100)
1312x=6500
6500 divided by 1312x
is 4.95%
OR what is the other method of doing this problem? Like solve for x (aka the unknown percentage here)? Besides using proportions how would you go about correctly translating this problem? for example when it say "what is(equals) the percentage of(multply) missing students on any given day? I think it means, 65(P)=1312
or 1312(P)=65
Is this the correct way to solve a problem like this?
65/1312 = x/100
1312x = 65(100)
1312x=6500
6500 divided by 1312x
is 4.95%
OR what is the other method of doing this problem? Like solve for x (aka the unknown percentage here)? Besides using proportions how would you go about correctly translating this problem? for example when it say "what is(equals) the percentage of(multply) missing students on any given day? I think it means, 65(P)=1312
or 1312(P)=65
That is correct. Your answer also makes sense because 10% of 1312 is 131, and 65 is a bit less than half of that.
7:47, 1/5 year??
I thought the <1/5 year was a typo...
Hay champ! You gotta be more active on KA. That is all that does remain, for you to get to MIT!
how do you know whether to multiply all the numbers together to get the measurement of mt. yukon or not? how do you know thats the way to find out?
Why 1/5 of a year?
He made an error. It is <1 year and > 1 year. As a teacher my mouth sometimes works faster than my brain. But his concept is correct.
how do you answer this? : 7x = 9y
Thanks! :D
Thanks! :D
between 1:27 and 2:02, why does 13x=5*6?
because 13/6 = 5/x and cross multiplication?
I don't get the mountain question. If Mont Blanc is 4800 meters high, than what is the size? It says mont elbert was 44/48 the SIZE of Mont Blanc. But what is the size? It doesn't tell me in the problem! :(
in a camp 180 students had ration for 20 days. how many students should leave the camp so thatthe same ration may last for 25 days?
30 students should leave the camp.... :)
all of the the video the guy goes to fast
Sylvia,
Use the pause button when you want him to stop so you can think about what he said.
And just click along the time stripe to go back a little if you want him to repeat something.
You have control at Khan Academy.
Use the pause button when you want him to stop so you can think about what he said.
And just click along the time stripe to go back a little if you want him to repeat something.
You have control at Khan Academy.
what is ratio what is proportion what is the difference
a ratio is, for example 4:9 but a proportion is 4:9=x:18 usually it is solve for x
why does it mention mount blane ate 3:32?
I dont get this at all it is to hard. =(
What if say the question is x3/(over)5=7/3
then d cross multiply and find it out
So, would the fraction 1/5 equal to the ratio 1:5?
This discussion area is not meant for answering homework questions.
At 7:45 and 8:43 I don't understand what he means by 1/5 year. Why isn't it just one year?
Well, he's just saying that it is 1/5 year, which is 2.4 months. Its just the problem.
i dont got it at 8:0110:24
This is not really a question, more like a shoutouy
Thanks for helping me pass my math and i might be able to move back up in my math class!!!
Thanks for helping me pass my math and i might be able to move back up in my math class!!!
I'm excited for you! That's exactly what's happening to me... sorta. I have a 69% right now and Sal, god of all math, made me understand a WHOLE lot more than my other teacher. Good luck with you :)
great job
Thats so true!! I am in love and I have driven myself crazy with the joy of it! Spread the word so more kids can learn!!!
awesome
Be kind to other students. You can vote ten times each hour you are working on the site. Remember to vote for good questions and answers both. Badges are awarded at 10, 25, and 50 up votes.
what is wrong the fact that they are looking towards mr. khan to get help?! they are getting better and i praise them for that!
all the best
please im tired:/
hey can i go to bed???:/
tahts wrong why because you did not do it right ok
in chemistry class, the girl to boy ratio is 9 to 3
if there are a totalof 60 students, how many girls are there?
from bai3006 the best gamer ever
if there are a totalof 60 students, how many girls are there?
from bai3006 the best gamer ever
at 4:11 working backwards, can u work this out another way besides working backwards?? if so how would we?
You know, I never really understood it when Sal multiplies a fraction a number, like in the beginning of the video. how did he multiply a fraction by x. I know how to multiply fractions, but I just can't seem to understand that. Help?
when he multiplies with x, the fraction he multiplied it by becomes opposite like... Example:(x times 3/4 = 4/3)
if u take 227/12 and 375/3 could make a proportion out of it?????
It wouldn't be an equal proportion, so nope.
What is a proportion?
How do you solve the problem at 2:47. I still don't understand how to solve these kind of problems.
in 0:06 how did he get the five?
He used the theory of quadratic's to solve then simplified the remainder of negative number's and got 5. Simple? >.>
That is just part of the problem. He didnt solve anything anything to get it.
What is the easy way to find out the answer
i don't get it
it is all so confusing! Please Please explain it again.:D
smiles,
Brezy Angel Froehlich (that is all random letters up there)
smiles,
Brezy Angel Froehlich (that is all random letters up there)
A portion is when you give food out depending on who is there by the table. A Proportion is a professional version of that, where you give out numbers from one equation to the other equation, making sure to depend on the rules of math, you don't want one of your equation guests getting all 'undefined' on you!
Just don't let the equations sit there all lonely. It's hard to go straight up you'll never convince a 2 on the bottom of 1/2 to climb over that roof. But diagnolly, any number can climb steps, even I can (and I weigh 220 lol). So Bring the lonely numbers from the bottom, to the tops diagnoly across, through the '=' elevator. Just make sure you do it to both numbers, or you end up with a very angry left out number, that will snitch on your teacher to get you marked wrong on the test!
Isn't Mont Blanc spelled wrong? Isn't it supposed to be Mount Blanc?
"Mont" is the French word for "mountain". It just happens to look similar to the English word "mount" because French and English both developed much of their vocabulary from Latin. In English the name means "White Mountain", but we just tend to call it "Mont Blanc" regardless.
It's spelled correctly.
http://en.wikipedia.org/wiki/Mont_Blanc
http://en.wikipedia.org/wiki/Mont_Blanc
this is a great way to learn how to set up porportions
Yeah its kindof like microsoft paint. if you look close he has like a little kite connected by tiny dots.
he does not use a mouse
How did he find the answer 6:40?
why is this so hard
Man, I Dont Not Understand .
What Would E And N Stand For ? A Number ?
there different then other ratios
you need to be advanced for this kind of math
you need to be advanced for this kind of math
A family has a total after tax income of $2400/month and a monthly mortgage expense of $800. find the ratio of mortgage expense to after tax income?
is it 80:240 the answer
This ratio would be 800:2400 or 800/2400, now just reduce the common factors.
how many killograms equals a gallon? i dont understand how to do this because one is volume and the other is mass
A gallon of water would have a different mass than a gallon of air or a gallon of mercury. You need to know the density to calculate kilograms per gallon.
But if the problem was "How many kilograms in a gallon of water", you can find a very close estimate.
A cubic centimeter of water has a mass of about 1 gram. A liter of water has a mass of about 1 kilogram. (Density of water varies with temperature, but 1 liter/1kg is a close approximation.)
So if the question was the mass of a gallon of water, you can use the following ratios to find your answer.
1 kg/1 liter
3.78541178 liters/ 1 gallon
I hope that helps
But if the problem was "How many kilograms in a gallon of water", you can find a very close estimate.
A cubic centimeter of water has a mass of about 1 gram. A liter of water has a mass of about 1 kilogram. (Density of water varies with temperature, but 1 liter/1kg is a close approximation.)
So if the question was the mass of a gallon of water, you can use the following ratios to find your answer.
1 kg/1 liter
3.78541178 liters/ 1 gallon
I hope that helps
Hi, at around 9:41, Sal puts the number of students that have a cell phone that is more than 1 year old (the 7/15 x) over the number of people that have cell phones (2/3 x). Can someone give me a bit of intuition about why this makes sense? Thanks in advance.
6/8,22/28?
using proportional reasoning.
using proportional reasoning.
whats agrivating me is why do you need to multiply anything times x? @00:29 whats the point?
Bob building a house and garage. the house, garage and driveway and a colour bond fence on three sides, leaving the from of the block unfenced.
have quotes for turf @$7.20 per square metre and colour bond fence @$92 per linear meter. advised to order an extra 5%for both, to allow for joins, short lengths and damaged turf.
find the cost of landscaping the block?
have quotes for turf @$7.20 per square metre and colour bond fence @$92 per linear meter. advised to order an extra 5%for both, to allow for joins, short lengths and damaged turf.
find the cost of landscaping the block?
what does ratio have to do with proportion? Sorry if it seems like a stupid question i just don't know.
A ratio shows the how the proportion works. A ratio such as 8:3 says that for every 8 of the first item, you will always have 3 of the other. In other words, say were were talking about weight: "These 8 oranges have the same weight as 3 of these big potatoes, so their weights are proportional to each other at a ratio of 8 to 3."
Okay a ratio is something like 5/2 now you can use this to make something like this: 5/2=10/x. The ratio was used to make a proportion. Here x=4 because 2*2=4
and 5*2=10.
and 5*2=10.
I don't understand which to multiply by: x or the number below/above x?
whats the difference of a ratio and a proportion
w+3/4=5 1/3
solve for w.
solve for w.
4 5/12 or 53/12
At 09:099:23, did he just just cross multiply?
Is this more complicated than it looks?
It's actually less complicated. You just look at the diagonals and multiply them. The products of the diagonals equal each other. Then you just solve!
A portion is when you give food out depending on who is there by the table. A Proportion is a professional version of that, where you give out numbers from one equation to the other equation, making sure to depend on the rules of math, you don't want one of your equation guests getting all 'undefined' on you!
Just don't let the equations sit there all lonely. It's hard to go straight up you'll never convince a 2 on the bottom of 1/2 to climb over that roof. But diagnolly, any number can climb steps, even I can (and I weigh 220 lol). So Bring the lonely numbers from the bottom, to the tops diagnoly across, through the '=' elevator. Just make sure you do it to both numbers, or you end up with a very angry left out number, that will snitch on your teacher to get you marked wrong on the test!
Maybe
nope
yes
Can you simplfiy the proportions before you cross Multiply ?
Yes, but only if both sides can be simplified.
HI SAL!! this video helped me understand ratios and propartins
How do you solve a ratio proportion with slope
could u specify the question?
how do u rewrite a quotient as s a ratio using the units in a denominator
what is the unknown number?
1/3 over 3/8, equals to 2/5 over the unknown number. what is the unknown number? how do i solve this problem/
1/3 over 3/8, equals to 2/5 over the unknown number. what is the unknown number? how do i solve this problem/
(1/3)/(3/8)=(2/5)/(x) // *x, /(1/3), *(3/8)
x=(2/5)*(3/8)/(1/3)
x=3*(2/5)*(3/8)
x=(6/5)*(3/8)
x=(6*3)/(5*8)
x=18/40
x=9/20
x=(2/5)*(3/8)/(1/3)
x=3*(2/5)*(3/8)
x=(6/5)*(3/8)
x=(6*3)/(5*8)
x=18/40
x=9/20
How do I find an actual ratio?
this takes a lot of time you need to be patient i guess
Just don't let the equations sit there all lonely. It's hard to go straight up you'll never convince a 2 on the bottom of 1/2 to climb over that roof. But diagnolly, any number can climb steps, even I can (and I weigh 220 lol). So Bring the lonely numbers from the bottom, to the tops diagnoly across, through the '=' elevator. Just make sure you do it to both numbers, or you end up with a very angry left out number, that will snitch on your teacher to get you marked wrong on the test!
MOST IMPORTANTLY: Sal wants us to get why cross multiplying works! It's just looking under the hood of the engine. Don't worry cross multiplying is the engine, it will always work! Cheers!
A portion is when you give food out depending on who is there by the table. A Proportion is a professional version of that, where you give out numbers from one equation to the other equation, making sure to depend on the rules of math, you don't want one of your equation guests getting all 'undefined' on you!
Hey, I'm having trouble solving 'continued ratios'
For example my problem would look like ;
A : B= 3 : 4 B : C= 3 : 2
What is the continued ratio;
A : B : C ?
For example my problem would look like ;
A : B= 3 : 4 B : C= 3 : 2
What is the continued ratio;
A : B : C ?
You would find the lowest common multiple between the common variable on one ratio and the common variable on the other.
For this particular example, you would do
A:B x 3 and B:C x 4
or
3 : 4 x 3 and 3:2 x 4
which equals 9 : 12 and 12 : 8, where A is 9, BOTH 12s are B, and C is 8.
From there, because B is common on both ratios, you can form a continued ratio of:
A : B : C = 9 : 12 : 8
For this particular example, you would do
A:B x 3 and B:C x 4
or
3 : 4 x 3 and 3:2 x 4
which equals 9 : 12 and 12 : 8, where A is 9, BOTH 12s are B, and C is 8.
From there, because B is common on both ratios, you can form a continued ratio of:
A : B : C = 9 : 12 : 8
If the total cost of x apples is b cents, what is a general formula for the cost, in cents,
of y apples?
of y apples?
why did he say the answer for yukon is 4 less than 300 when i was 4 less than 600
what does x stand for
x stands for the unknown in your equation. If we have the problem x/4=2/8, we have to solve to find x.
This video makes no sense to me. I need help ;[
Just don't let the equations sit there all lonely. It's hard to go straight up you'll never convince a 2 on the bottom of 1/2 to climb over that roof. But diagnolly, any number can climb steps, even I can (and I weigh 220 lol). So Bring the lonely numbers from the bottom, to the tops diagnoly across, through the '=' elevator. Just make sure you do it to both numbers, or you end up with a very angry left out number, that will snitch on your teacher to get you marked wrong on the test!
A portion is when you give food out depending on who is there by the table. A Proportion is a professional version of that, where you give out numbers from one equation to the other equation, making sure to depend on the rules of math, you don't want one of your equation guests getting all 'undefined' on you!
How come at 7:48 its < 1/5 yr cell phone?
in half an hour the bucket is 1/5 of the way full. What is the rate at which the water is leaking?
does this pair of ratios form a proportion 3.5/1.2=7/8
These proportions are very hard
Why is fractions different from proportions.
what is 2 plus 2
what is the numbers for the mathamatical sequence pie
pi? 3.14159265
How pressure can be calculated if only height is given ?
Please help.
Thank you.
Please help.
Thank you.
how do i set up this question using ratios? Fanny and Kevin shared a box of markers in the ratio 5:3; fanny gave half of her share to Kevin. Kevin then had 30 more markers than fanny. How many markers did fanny give to Kevin?
I do not understand where you got your formula: K+(1/2*F)  1/2*F=30
Now K+(1/2*F)  1/2*F=K. Please make it simpler.
Now K+(1/2*F)  1/2*F=K. Please make it simpler.