Fractions

# Adding and subtracting fractions with unlike denominators

## How to add fractions that have different denominators

To solve this problem, we need to find the least common multiple to get at the common denominator. Can you help? We bet you can!
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## How to add fractions that have different denominators

Discussion and questions for this video
why does the denominator have to be the same as the other denominator
i agree it is good explanation
What does it mean to simplify the problem?
Simplifying a fraction just means putting it into the simplest form. For example, 3/6 can be simplified to just 1/2. They are the same thing, but 1/2 is simplified.
Does anyone get this?
Ya its pretty basic math find equal denominators and add!
I already knew how to do this, but it gave me a couple pointers.
if 12x3 is 36 then why did he not do 9x3
What do you mean?
no because that would not make sense
at the end do you have to divide the numbers
If you're talking about 3:45 then no.
Why does the denominator have to be the same as the other denominator?
Think of it this way:

When you are adding or subtracting two things, they must be the same in order to make it work. If you had 6 basketballs, could you subtract 3 iPhones from them? Of course not!

When working with fractions, the denominator describes the SIZE of the piece, so to do the addition or subtraction, you must make them the same size.

The numerator tells you HOW MANY of each "size" you have, so you only add or subtract the numerator, not the denominator (you aren't changing the "size" of the pieces).

Hope this helps.
1 Comment
Mrs Dyer baked 5 1/2 batches of brownies. She needed 3/4 cups of vegetable oil for each batch she makes. How much vegetable oil will she bake her brownies?
math is good i love math ( ͡° ͜ʖ ͡°)
how would you break own 3/5 + 1/11
3/5 + 1/11 = 38/55.
If you understand about adding the fractions together, and changing the denominators, see the video on subtracting fractions. (http://www.khanacademy.org/math/arithmetic/fractions/v/subtracting--fractions). There isn't one specifically on subtracting fractions with unlike denominators.
1 Comment
why do you need to multiply the numerator when you multiply the denominator to add or subtract fractions?
Good question. The answer is that if you didn't then you would change the value of the fraction. Like 2/3. If you multiplied both of them by 2, you would have 4/6. Both equal 0.66. If you multiplied the bottom only, then it would be 2/6 which is equal to 0.33. It would change the value.
why do we use the same denominators, when we are doing the adding when we have a different denominators.
You can't add 5 pizzas to 10 Jupiters.
can both fractions be negativs
Right Patrick Crandon!
why do you have to find a common denominator?
math is good i love math ( ͡° ͜ʖ ͡°)
I like fractions?
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1 Comment
This should be in the tip/thanks section. (I am not a moderator, but I'm pretty sure this is against the rules as irrelevant)
Fractions are so fun!
1 Vote
1 Comment
math is good i love math ( ͡° ͜ʖ ͡°)
what to do with 7/6
math is good i love math ( ͡° ͜ʖ ͡°)