Subtract 4/40 from 72/21, Solve 3 9/21

Subtract 4/40 from 72/21

1^st number: 3 9/21, 2^nd number: 4/40

72/21 - 4/40 is 233/70.

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,
72/21 = 72 × 40/21 × 40 = 2880/840
Likewise, for the 2nd fraction, since 40 × 21 = 840,
4/40 = 4 × 21/40 × 21 = 84/840
Subtract the two like fractions:
2880/840 - 84/840 = 2880 - 84/840 = 2796/840
After reducing the fraction, the answer is 233/70
In mixed form: 323/70

MathStep (Works offline)

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