Add 72/90 and 28/21, Solve 72/90 + 1 7/21 as a fraction

Add 72/90 and 28/21

1^st number: 72/90, 2^nd number: 1 7/21

72/90 + 28/21 is 32/15.

Find the least common denominator or LCM of the two denominators:
LCM of 90 and 21 is 630

Next, find the equivalent fraction of both fractional numbers with denominator 630
For the 1st fraction, since 90 × 7 = 630,
72/90 = 72 × 7/90 × 7 = 504/630
Likewise, for the 2nd fraction, since 21 × 30 = 630,
28/21 = 28 × 30/21 × 30 = 840/630
Add the two like fractions:
504/630 + 840/630 = 504 + 840/630 = 1344/630
1344/630 simplified gives 32/15
So, 72/90 + 28/21 = 32/15
In mixed form: 22/15

MathStep (Works offline)

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