Subtract 20/40 from 7/21, Solve 7/21

Subtract 20/40 from 7/21

7/21 - 20/40 is -1/6.

Find the least common denominator or LCM of the two denominators:
LCM of 21 and 40 is 840

Next, find the equivalent fraction of both fractional numbers with denominator 840
For the 1st fraction, since 21 × 40 = 840,
7/21 = 7 × 40/21 × 40 = 280/840
Likewise, for the 2nd fraction, since 40 × 21 = 840,
20/40 = 20 × 21/40 × 21 = 420/840
Subtract the two like fractions:
280/840 - 420/840 = 280 - 420/840 = -140/840
After reducing the fraction, the answer is -1/6

MathStep (Works offline)

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