Subtract 15/80 from 28/21, Solve 1 7/21

Subtract 15/80 from 28/21

1^st number: 1 7/21, 2^nd number: 15/80

28/21 - 15/80 is 55/48.

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

Next, find the equivalent fraction of both fractional numbers with denominator 1680
For the 1st fraction, since 21 × 80 = 1680,
28/21 = 28 × 80/21 × 80 = 2240/1680
Likewise, for the 2nd fraction, since 80 × 21 = 1680,
15/80 = 15 × 21/80 × 21 = 315/1680
Subtract the two like fractions:
2240/1680 - 315/1680 = 2240 - 315/1680 = 1925/1680
After reducing the fraction, the answer is 55/48
In mixed form: 17/48

MathStep (Works offline)

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