Subtract 21/9 from 81/80, Solve 1 1/80

Subtract 21/9 from 81/80

1^st number: 1 1/80, 2^nd number: 2 3/9

81/80 - 21/9 is -317/240.

Find the least common denominator or LCM of the two denominators:
LCM of 80 and 9 is 720

Next, find the equivalent fraction of both fractional numbers with denominator 720
For the 1st fraction, since 80 × 9 = 720,
81/80 = 81 × 9/80 × 9 = 729/720
Likewise, for the 2nd fraction, since 9 × 80 = 720,
21/9 = 21 × 80/9 × 80 = 1680/720
Subtract the two like fractions:
729/720 - 1680/720 = 729 - 1680/720 = -951/720
After reducing the fraction, the answer is -317/240

MathStep (Works offline)

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