Subtract 81/21 from 18/80, Solve 18/80

Subtract 81/21 from 18/80

1^st number: 18/80, 2^nd number: 3 18/21

18/80 - 81/21 is -1017/280.

Find the least common denominator or LCM of the two denominators:
LCM of 80 and 21 is 1680

Next, find the equivalent fraction of both fractional numbers with denominator 1680
For the 1st fraction, since 80 × 21 = 1680,
18/80 = 18 × 21/80 × 21 = 378/1680
Likewise, for the 2nd fraction, since 21 × 80 = 1680,
81/21 = 81 × 80/21 × 80 = 6480/1680
Subtract the two like fractions:
378/1680 - 6480/1680 = 378 - 6480/1680 = -6102/1680
After reducing the fraction, the answer is -1017/280

MathStep (Works offline)

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