How do you add fractions with different denominators?

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• Anonymous

u gotta make common denominators.......like if u have 1/4 and 1/2 then u take 1/2 and multiply the numerator and th denominator by 2 so its 2/4 and then u just add it together......=3/4!

Source(s): SCHOOL!!!
• 1 decade ago

You convert them to a common denominator. Sometimes it's easy - 1/2 + 1/4 for example, you would convert the 1/2 to 2/4 so both denominators were 4, then add the numerators, which would give you 3/4 for an answer.

Some are a little more difficult. 4/5 and 3/4 for example.

To find a common denominator for these two, you can always multiply the two denominators together - in this case, you would have a denominator of 20. Multiply the 4 in the 4/5 by 4 (the other denominator - it's called cross multiplying) and you get 16/20. Multiply the 3 in 3/4 by 5 and you get 15/20.

Add 15/20 and 16/20 and you get 31/20.

Then reduce to a mixed number, and your answer is 1 and 11/20.

Does that help?

• T
Lv 4

first make it so that the denominators become the same

for example

3/5 + 5/3

you have to multiply 3/5 and 5/3 both by a equivalent of 1

multiply 3/5 by 3/3 which makes it 9/15

then multiply 5/3 by 5/5 which is 25/15

then do 9/15 + 25/15 ----> 34/15 and simplify from here