Subtract 42/45 from 8/21, Solve 8/21

Subtract 42/45 from 8/21

8/21 - 42/45 is -58/105.

Find the least common denominator or LCM of the two denominators:
LCM of 21 and 45 is 315

Next, find the equivalent fraction of both fractional numbers with denominator 315
For the 1st fraction, since 21 × 15 = 315,
8/21 = 8 × 15/21 × 15 = 120/315
Likewise, for the 2nd fraction, since 45 × 7 = 315,
42/45 = 42 × 7/45 × 7 = 294/315
Subtract the two like fractions:
120/315 - 294/315 = 120 - 294/315 = -174/315
After reducing the fraction, the answer is -58/105

MathStep (Works offline)

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