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## Adding and subtracting fractions with unlike denominators

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## Adding fractions with unlike denominators

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why does the denominator have to be the same as the other denominator
Good question.
In mathematics, the concept of adding and subtracting fractions require the denominator to be common. The numerator does not need to be common but the denominator must be.
If the denominator wasn't common how would we work out the question?
E.g. 1/3 + 3/7 = ?
To work out this question, we would have to find the LCM (Lowest Common Multiple) of the denominators; in this case, 3 and 7. Then when we find that it is 21, we can adjust the numerators to 7 and 9. With that done, we can add 3 and 7 to make 10 over the denominator, which is 21.

This is why the denominators have to be common. There was no equation or formula built in the concept of adding and subtracting fractions that do not require the denominators to be common.

I hope this clears everything up. :)
Why did he say to turn the nine in to a 36 and why multiply by 4 what.]
nine times four is thirty six but why cant the nine just be nine. I'm confused ):
and why do we have to multiply the numerator by 4 too.~_~
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to add fractions, you need to have the denominator the same. these two fractions have denominators of 9 and 12. The lowest common multiple of these two numbers is 36. That requires multiplying by x4 and x3 respectively. We multiply the numerator and denominator by the same number so the number does not change.
4/9 * 4/4 = 16/36. 4/4 is the same as 1, so the number doesn't change
If both denominators are prime numbers, is the only least common multiple between them always going to be the product of the two?
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Well, yes because since both are prime numbers, and prime numbers can't divide into each other's multiples, it will have to be the product. For example, 1/5 + 1/7, 7 can't divide into 5's multiples and 5 can't divide into 7's multiples, so the denominator has to be the product. By the way the answer is 7/35 + 5/35 = 12/35
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Why do the denominators have to be the same?
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You do not have to make them the same but it makes it far easier to do.
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why does the denominater have to be greater than the top number?
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Excellent question my friend. If you had two fractions like 6/5 and 7/5 you would get 13/5. That is what you would call a improper fraction. In arithmetic you wouldn't leave it like that because it's considered a improper fraction. You would need to change it into a mixed number. When you get to algebra 1 they will allow you to leave it as a improper fraction as an answer to a problem.
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I don't get this it is hard can anybody help me?
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it is quite simple if you ask me all you have do is this Whenever you add fractions with unlike denominators, you must make the denominators of the same value. In this example, the easiest approach is to multiply 8 x 3 to get 24. Here, you multiply by 3 to get . Then you multiply the second equation by 8 to get . Note that both addends have 24 as a denominator. Add in the same manner as with the unit Adding fractions with like denominators.
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can you divide fractions
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yes you can beacuse fractions are the answer of 1 divide by a number so yes they can
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i cant understand this, how did you get the x3 but the other x4?
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Because it is a fraction you can multiply it by anything - it will still be the same fraction of a whole number. (1/2 * 2 is 2/4 - but both are 0.5 in decimal terms)

The objective is to get the denominators the same.
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What if you have a problem where one of the fractions has to be divided into a fraction, and the other number is whole?
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If one number is whole, you put it over a denominator of 1. If you have 24/8 - 2, write:
24/8 - 2/1
Hope this helps!
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Is multiplying a fraction as easy as adding and subtracting one?
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Multiplying is even easier because you don't have to find any common denominators or anything. You just multiply across: the numerator times the numerator and the denominator times the denominator.
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can both fractions be negativs
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Right Patrick Crandon!
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Well when you add a fraction like 4/6 and 9/10 you have to get a common denominator. To do that multiply the denominator 6x10= 60 now the fraction would look like _/60 all we need to do is fine the numerator 6x what = 60 its 10 then we do 10x4 to get the numerator 40/60 do the same thing to the other one now we got 54/60 + 40/60 ok add the numarator 54+40=94 so now we got 94/60 we need t turn it into a mixed number. How much times can 94 go into 60 its 1 time so now we have 1 and 34/60 and thats not your answer yet you have to reduce. So divided by 2 = 17 then 60 divided by 2 is 30 so 17/30.
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I DOn't Get It
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When numerator is greater than the denominator.. it is considered as improper fraction?
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Yes it is a improper fraction so you need to turn it into a mixed number.
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what if the denominators of two fractions don't have a least common multiple
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you work with them in the way as they are - they are already simplified ;)
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we are doing this in math and i kinda understand it but its hard also
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Agreed, I still think fractions is a pain in the neck, but just work hard and you'll understand it.
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i think you can also just multiply the denominaters by each other........right?
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yes, you can just multiply the denominators by each other, but when you use larger numbers, it becomes tedious to multiply all of those giant numbers. It is much simpler to work with smaller numbers, and you are less likely to make a mistake that way. Multiplying the two numbers together is sometimes the only way to get a common denominator.
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This website has helped me a lot in my school work. Although i am a little confuzzled on how he got his answer, like how did he turn it to a mixed #?
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Take a improper fraction like 4/3. Divide the denominator by the numerator. That's 1. How much is left? 1/3, so the mixed number is 1 1/3. This problem doesn't need simplifying, but remember to in other problems if they need it. Hope this helps.
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why does the denominator have to be the same?
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The denominator has to be the same because then it makes it easier to add, subtract, multiply, or divide the fraction.
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I do not get the mixed fractions, is there an easier way
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What don't you understand about them?
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What if both numbers don't have a greatest common factor?
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Hi William. Two numbers always have a greatest common factor. Sometimes, it is 1, but often it is larger.
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do you have fractions with multiplication
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Yes they do have fractions with multiplication khan academy.
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what is he trying to say? it is confusing.
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it is, why doesn't it have audio
what if there was an x in the denominator like in the problem 1/x + 4/1
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That is a more advanced type of problem, but you can still find a common denominator.
you could multiply 4/1 by x/x and get 4x/x
then add the numerators 1 + 4x, which can't be simplified further.
So the new form is the (1 + 4x)/x also written as

1 + 4x
--------
x

This isn't really any simpler than the previous expression but they are equal.
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What if the Denominator was different from the other Denominator?

O_o
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That's what were talking about here. "Unlike Denominators" are fractions with- literally- Unlike denominators.
Try the Skill "Adding Fractions" when you're done!
This is too fast can you slow down?
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If it goes too fast you can always pause the video or rewatch it. Hope this helps!
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What I don't get is 36/49= 0.7... I have to make it 1? And if it was 0.5?
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I need help with dividing fractions how do I do that
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Ex: 1/2 divided by 3/4
You will flip 3/4 and the dividing sign will be multiplying sign, so it will be 1/2 multiplied by 4/3 so the answer will be 2/3.
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Can u multiply it with a bigger denominater ?
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Sure, you can use any denominator you want, as long as they are common. Then reduce at the end for the last step. Tip: See the recognizing divisibility video. It is very helpful.
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i dont get it why does the denominator have to be the same as the other denominator? (:
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why do u need to do a common denominator
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u are soo smart.. just what i need to no except can you do a vidio were you can like turn the inproper fraction into a proper one?? if that makes sence
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hey jcnz2011 u boy or girl
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2 3/4 +3 15/28
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you cant answer that it dosent make sense fractions only
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Make a video that tells me how to simplify a fraction that is NOT an improper fraction!
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why do you have to have the sam e denominator
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the denominator of a fraction is its place value and the numerator is the digit .
when we add we must add digits with the same place value.
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would is easier for you guys to complete 4/5 + 6/7 or 5/6 +1/2?
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I don't understand. This just confuses me. Can anyone turn this video into something that a 13 yr. old can understand?
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I grasped this concept when I was 8. You'll get it, just keep trying.
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But what if you get a improper fraction do you have to turn it into a mixed number or can you just let it be.
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If your asked to "simplify" the answer, turn it into an improper fraction. Other than that, it depends on whether or not your teacher wants you to.
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what did he say I still don't get it
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it is conufseing me i don't now why
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i still dont get nothing by the way dont put my question at the bottom
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thax f4 the help
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So how would you do a question like 1/4 - 3/12 ?
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Find the least common factor of the denominators (twelve here), find out what to multiply the numerator AND denominator with to achieve a denominator of twelve, i.e. three for the first fraction and one for the second.

Then do the subtraction.

Easy Peasy!
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Okay so this is today's homework is about that and I haven't really get what I had to do so look at this problem 1/3 + 5/9 they both can't reduce! or unless you can do the factor tree on 1 and 3 okay never mind thank you for doing this video I really didn't understand Adding Fractions with Unlike Denominators. and plus is their ever gonna be a problem with dividing? Like with unlike denominators?
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To add fractions, find the least common denominator (LCD). Here, it would be 9.

1) You can convert 1/3 to 3/9. So you end up with 1/3 + 5/9 = 3/9 + 5/9.
2) Add the numerators. (3+5)/9 = 8/9.
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ok this will be a question but does anyone have mrs sullivan for math at mckinley elementary ok if so what is tha simplest form of 2/3-1/9?
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idk
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Why are both the denominators the same?
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If you want to add or subtract a fraction, you have to make both side have the same denominator.
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Why would you not simplify this answer, 22/21 to 1 1/21?
The problem was 5/7 + 1/3. In my homework book it said the answer was simply 22/21.
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How do you simplify it if it is not an improper fraction?
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the whole thing was confusing
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Is there any other faster ways to do the problems instead of just wasting so much time on only one problem when i could be on the next one in just a minute or less?
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Get the LCD(least common denominator) of the denominator then add. He explains things that is why the video is long..:)
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Why do we have to find a common multiple? Why cant we just the numerators and the denominators together, like we multiply the numerators and the denominators when we are multiplying fractions. I'm confused. Help!

Thanks,
Tesla
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tell me the answer to this 56/93 + 43/94
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This section inst for doing your home work.
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is there any videos on subtracting fractions with different denominators
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vote-if u agree that the person who made this website is trying to turn the unlike denominator into a common denominator to make it more easier
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Can u write a fraction like this -5/9?
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I thought you have to divide 36 to 4/9 and to 11/12 ???
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this video has helped me like sooooooooo much. THANKS SAL!
ttyl
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no prob!!!!!!!!!!!!!!
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can you show an ex. of m-5 over m squared+9m+20 +4m-1 over m squared +7m+10 ?
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How do you add fractions with unlike fractions can anyone give me some steps
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where are the problem exercises?
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why do you make it so complicated?
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I don't get why we have to multiply
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can you please teach me calculus ?
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That's in the calculus section.
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i dont get it
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When I search for hint. It does not seems well And i Gotta do my math right now. BYE EVERYONE
BYE ,
FROM
TYLER HALL
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WOW GREAT SEE THE VIDEO
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when you subtract the fraction do you have to slimply it ?
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how did you know to multiply in the begging of the video
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i am in 4th grade and i loved the way u teach in a simplified manner.
where can i find problems to solve adding fractions with unlike denominators.
thx
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i don't understand this formula its a little bit tricky.can some one help me.
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Why do we have covert mixed numbers to improper fractions?
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why do you have to multiply by the same number
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You have to multiply the same number for the denominator and numerator because whatever you do to the bottom, you do to the top. If you don't do this your fraction would not be equivalent so you would get a different answer because you changed the value of the fraction completely. Hope this helped. :)
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why can't you add them wit the denomenator that the # come with
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at2:00 how does it work
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If you mean by counting the multiples of 9 to find one that is divisible by 12, you can check every single one (but it's not very efficient), or you can learn the multiples of 9 and 12 up to a certain point. If you mean the multiplying of the denominator as well as the numerator, my teacher always says: "what you do to the bottom you do to the top!" so you make an equivalent fraction.
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how would you multiply 5/20 * 8/5
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Well you would cancel some of the numbers. the 5 and the 5 could cancel out, and that would leave you with 8/20.
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u are soo smart.. just what i need to no except can you do a vidio were you can like turn the inproper fraction into a proper one?? if that makes sence
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how do u add and subtracted fractions
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I do not understand this?
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i thought that you had to add the different denominators but you have to divide them
so when your multiplying do you have to divide the different denominators and so when your dividing different denominators you have to multiply them
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When you find a common denominator are you allowed to divide instead of multiply 9x2=18 ,9x3=27and blah blah blah ?
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Why does it have to be unlike denominators?
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what should i do if my fraction is 9/11+6/10
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This looks hard can some one help?
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i figured it out! it's easy
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Add My Bro as Couch: ¸„ø¤º°¨°º¤ø„¸¸„ø¤º°¨
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is there any way to do it without changing the denominators?
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Why do the denominators have to be the same?
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how about if we have like 36, and we have to find a GCF, and we have to do 2. what can save me from doin all that work?
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i dont know but good question.
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When subtracting mixed fractions, what if the second fraction is larger than the first? Like 7 3/5 - 5 4/5 = ?
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I don't understand. Why do you have to multiply the numerator?
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You want the new fraction to be equivalent to the original one so that the sum of the two fractions doesn't change. To do that, you need to multiply the numerator and denominator of the fraction by the same number.
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why is this so hard i kinda understand but not really who agrees
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Is it possible for there to not be a common denominator ?
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I don't really understand how to simplify. It is confusing to me somehow and everytime I get a question that asks me to simplify I can't do it, I don't understand it. Can somebody please help me figure it out?
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I was going through the adding mixed fractions with unlike denominators and simplifying them to their lowest term and I am so lost right now. I had to watch the videos like five times. I am just trying to figure it out.
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10,020,396 over 300,285,932 plus 125 over 70,000,000. Seems hard. bet you I can fool ya. :)
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If the denominator of both numbers are prime then why can't 1 be divisible by that prime number?
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can anyone give an example of what he means
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You have to fined a number that goes in to the denominators evenly.... i think Not sure!
Hope that helps
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what is common denominator in 6/7 + 8/21
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How did you get the x 4 and x 3?
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How would you do it it you had variables in different spots of the equation still adding and subtracting fractions with unlike and like denominators?
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Why is this so difficult?
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If you work harder, it will be easier.
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Why does the numorator have to be on the top and the denominator have
to be on the bottom?
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Hi, I was wondering if you were going make 49/36 into a proper fraction like he did... it there any other possible way of doing that? Or is that the only way to covert the improper fraction into a proper fraction? Just wondering! Thanks!
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Why Does This Video Have To Be So Short?
I Don't Understand!
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why do we need to know this?
how can this help us in the future?
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Report a mistake in the video
Example:

At 2:33, Sal said "single bonds" but meant "covalent bonds."

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