Subtract 21/84 from 90/20, Solve 4 10/20

Subtract 21/84 from 90/20

1^st number: 4 10/20, 2^nd number: 21/84

90/20 - 21/84 is 17/4.

Find the least common denominator or LCM of the two denominators:
LCM of 20 and 84 is 420

Next, find the equivalent fraction of both fractional numbers with denominator 420
For the 1st fraction, since 20 × 21 = 420,
90/20 = 90 × 21/20 × 21 = 1890/420
Likewise, for the 2nd fraction, since 84 × 5 = 420,
21/84 = 21 × 5/84 × 5 = 105/420
Subtract the two like fractions:
1890/420 - 105/420 = 1890 - 105/420 = 1785/420
After reducing the fraction, the answer is 17/4
In mixed form: 41/4

MathStep (Works offline)

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