Subtract 15/80 from 21/42, Solve 21/42

Subtract 15/80 from 21/42

21/42 - 15/80 is 5/16.

Find the least common denominator or LCM of the two denominators:
LCM of 42 and 80 is 1680

Next, find the equivalent fraction of both fractional numbers with denominator 1680
For the 1st fraction, since 42 × 40 = 1680,
21/42 = 21 × 40/42 × 40 = 840/1680
Likewise, for the 2nd fraction, since 80 × 21 = 1680,
15/80 = 15 × 21/80 × 21 = 315/1680
Subtract the two like fractions:
840/1680 - 315/1680 = 840 - 315/1680 = 525/1680
After reducing the fraction, the answer is 5/16

MathStep (Works offline)

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