How do you subtract dissimilar fraction?

Answer 1

You make the denominators the same, by multiplying the fractions by the denominator of the other fraction. Then you can subtract them.

For example, 4/5 - 7/8. Make the denominators the same by multiplying "4/5" by 8/8*, which gives 32/40. Multiply "7/8" by 5/5*, which gives 35/40. Denominators are now the same, so subtract: 32/40 - 35/40 = -3/40.

* 8/8 and 5/5 are each equal to 1, so you aren't changing the value of the fraction.

Sometimes it makes the calculation easier to find the lowest common denominator (LCD) first:

7/24 - 5/36 = ?

The LCD is 72 ... it's the smallest number that both 24 and 36 go into evenly. 24x3 = 72, and 36x2 = 72, so:

7/24 x 3/3 - 5/36 x2/2 = 21/72 - 10/72 = 11/72.

Answer 2

Before fractions can be subtracted or added, they must have the same denominators. Therefore, each of the denominator and numerator of a pair of dissimilar fractions should be multiplied by a number chosen so that the resulting fractions will have the same denominators. This is most readily accomplished by multiplying each fraction by the denominator of the other. Once the fractions have a common denominator, their numerators can be subtracted or added to obtain the proper value of the numerator of the sum or difference, which will have the common denominator thus determined. It may, of course, be possible to simplify the resulting fraction.