Subtract 2/12 from 72/21, Solve 3 9/21

Subtract 2/12 from 72/21

1^st number: 3 9/21, 2^nd number: 2/12

72/21 - 2/12 is 137/42.

Find the least common denominator or LCM of the two denominators:
LCM of 21 and 12 is 84

Next, find the equivalent fraction of both fractional numbers with denominator 84
For the 1st fraction, since 21 × 4 = 84,
72/21 = 72 × 4/21 × 4 = 288/84
Likewise, for the 2nd fraction, since 12 × 7 = 84,
2/12 = 2 × 7/12 × 7 = 14/84
Subtract the two like fractions:
288/84 - 14/84 = 288 - 14/84 = 274/84
After reducing the fraction, the answer is 137/42
In mixed form: 311/42

MathStep (Works offline)

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