Subtract 18/21 from 18/40, Solve 18/40

Subtract 18/21 from 18/40

18/40 - 18/21 is -57/140.

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

Next, find the equivalent fraction of both fractional numbers with denominator 840
For the 1st fraction, since 40 × 21 = 840,
18/40 = 18 × 21/40 × 21 = 378/840
Likewise, for the 2nd fraction, since 21 × 40 = 840,
18/21 = 18 × 40/21 × 40 = 720/840
Subtract the two like fractions:
378/840 - 720/840 = 378 - 720/840 = -342/840
After reducing the fraction, the answer is -57/140

MathStep (Works offline)

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