Subtract 9/21 from 81/20, Solve 4 1/20

Subtract 9/21 from 81/20

1^st number: 4 1/20, 2^nd number: 9/21

81/20 - 9/21 is 507/140.

Find the least common denominator or LCM of the two denominators:
LCM of 20 and 21 is 420

Next, find the equivalent fraction of both fractional numbers with denominator 420
For the 1st fraction, since 20 × 21 = 420,
81/20 = 81 × 21/20 × 21 = 1701/420
Likewise, for the 2nd fraction, since 21 × 20 = 420,
9/21 = 9 × 20/21 × 20 = 180/420
Subtract the two like fractions:
1701/420 - 180/420 = 1701 - 180/420 = 1521/420
After reducing the fraction, the answer is 507/140
In mixed form: 387/140

MathStep (Works offline)

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