Subtract 20/15 from 8/21, Solve 8/21

Subtract 20/15 from 8/21

1^st number: 8/21, 2^nd number: 1 5/15

8/21 - 20/15 is -20/21.

Find the least common denominator or LCM of the two denominators:
LCM of 21 and 15 is 105

Next, find the equivalent fraction of both fractional numbers with denominator 105
For the 1st fraction, since 21 × 5 = 105,
8/21 = 8 × 5/21 × 5 = 40/105
Likewise, for the 2nd fraction, since 15 × 7 = 105,
20/15 = 20 × 7/15 × 7 = 140/105
Subtract the two like fractions:
40/105 - 140/105 = 40 - 140/105 = -100/105
After reducing the fraction, the answer is -20/21

MathStep (Works offline)

Download our mobile app and learn to work with fractions in your own time:
Android and iPhone/ iPad