Subtract 21/18 from 3/21, Solve 3/21

Subtract 21/18 from 3/21

1^st number: 3/21, 2^nd number: 1 3/18

3/21 - 21/18 is -43/42.

Find the least common denominator or LCM of the two denominators:
LCM of 21 and 18 is 126

Next, find the equivalent fraction of both fractional numbers with denominator 126
For the 1st fraction, since 21 × 6 = 126,
3/21 = 3 × 6/21 × 6 = 18/126
Likewise, for the 2nd fraction, since 18 × 7 = 126,
21/18 = 21 × 7/18 × 7 = 147/126
Subtract the two like fractions:
18/126 - 147/126 = 18 - 147/126 = -129/126
After reducing the fraction, the answer is -43/42

MathStep (Works offline)

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