how do you subtract fractions with different denominators?

Answer 1

Find a common denominator. Something that both can multiply to become. Like 4 and 5 and multiply to be 20. The question is 3/4 - 2/5. You multiply to get a common denominator. You get 15/20 - 8/20 = 7/20

Answer 2

Multiply to make the denominators the same. For example if you have 3/4 - 1/8, you would have to multiply 3/4 by 2 so the denominator would be equal to 8. The new fraction would be 6/8 - 1/8, then you can do the problem.

If there is no immediate common number like the problem above, you need to look at the multiples for each number. For example, 2/3 - 1/5.
Multiples of 3 are 3, 6, 9, 12, 15, 18, 21...
Multiples of 5 are 5, 10, 15...
You can stop once you find one that matches.
For this you would multiply 2/3 by 5, and 1/5 by 3.
The new fractions would be 10/15 and 3/15
The new problem is 10/15 - 3/15.

Hope that all makes sense.

Answer 3

well, i am real good at that(not to brag or anything)but well, lets say you had this as a problem.....
10
--------
24


9
---------
- 36
well first what u have to do is find the leat common denominator . to do this, you think,what numbers do these have in common? it just so happens that 24 and 36 can both be divided in 12! so, if 12 times 2= 24, you would have to divide the top number by 2, because whatever you do to the bottom, you do to the top!, so first you must divide 10 by 2 and this fraction then becomes 5 over 12. for the next one, 12 times 3= 36, therefore whatever you do to the bottom u must do to the top. this fraction then becomes 3 over 12. Now you can subtract like normal! 5-3= 2, (everyone should know that!) and you keep the denominator as 12.the ending fraction becomes 2 over 12.(the next part you dont always have to do, but sometimes its required.) next you must simplify.so.... 2 and 12 must be divided by the same number to simplify(or reduce) the problem. you just have to find the least common multiple( which just means the lowest number the can possibly have in common beside 1 or 0.sometimes it can be as high as 5 or 7!) so 2 and twelve happen to have 2 the least common denominator, so you divide each by 2. 2divided by 2 = 1, and 12 divided by 2=6. your last and final fraction becomes....

1
-----------
6 ! (i know its a long process, but trust me, its pretty easy after you get the hang of it!)

Answer 4

Let's use the following fractions:

3/4 - 2/5 =

Before we can subtract the fractions, we need to get the denominators to be the same. To do this, first we must find the LCD, or Least Common Denominator -- the smallest number that both denominators divide evenly into.

To find the LCD, take the first denominator and multiply it by 1, 2, 3 etc. until you multiply it by the other denominator. Then do the same to the second denominator, until you multiply it by the first denominator. The LCD is the lowest number that appears on both list.

For our example the LCD is 20. It is 4x5 in the first and 5x4 in the second

Now modify the fraction using the LCD to make them like fractions

(3x5)/(4x5) - (2x4)/(5x4) = 15/20 - 8/20 = 7/20

For more help on these type of problems you can use my free website http://www.college-cram.com

Answer 5

1. find a least common denominator of the 2 different denominators and then follow the operation which in this case is subtraction

2.Example

4/5-1/3=?

1.15 is the least common denominator

5 goes into 15 3 times so you multiply 4/5 by 3 in the numerator and denominator
4/5 x 3/3=12/15
3 goes into 15 5 times multiply numerator and denominator by 5 1/3 x 5/5=5/15

Subtract the 2 like fractions
12/15-5/15= 7/15

Answer 6

you need to get a common denominator first. For example if the question is 2/3 - 1/4, you have to put them both over a common denominator such as 12. So the question would then become 8/12 - 3/12. the answer is 5/12.

Answer 7

the 1st subject to do is discover an common denominator. interior the 1st occasion it truly is 18. Then convert the fractions. the 1st occasion could be 15/18 + sixteen/18. then you truly upload the numerators and you get 31/18. Then simplify the fraction to a million 13/18. the 2d occasion could be 6 as an common denominator. Convert to 5/6 - 4/6. Then subtract the numerators: a million/6

Answer 8

Make them all have the same denominator I guess.

Eg: 9/16 - 3/4

there are 4 x 4 in 16, so multiply the top number by 4 as well, so you get 9/16 - 12/16

I think that's how you do it, I did it 20 years ago and there's been plenty of partying since then... :)

Answer 9

You look at the denominators then see what number they both have in common.After you do that you times the denominator with a number that to get the same number for both denominators ,but what you times to the denominator you have to do the same with the numerator.

Answer 10

You need to convert the fractions first so they have a common denominator....the same thing you do if you want to add fractions with different denominators.