Add 21/70 and 70/72, Solve 21/70 + 70/72 as a fraction

Add 21/70 and 70/72

21/70 + 70/72 is 229/180.

Find the least common denominator or LCM of the two denominators:
LCM of 70 and 72 is 2520

Next, find the equivalent fraction of both fractional numbers with denominator 2520
For the 1st fraction, since 70 × 36 = 2520,
21/70 = 21 × 36/70 × 36 = 756/2520
Likewise, for the 2nd fraction, since 72 × 35 = 2520,
70/72 = 70 × 35/72 × 35 = 2450/2520
Add the two like fractions:
756/2520 + 2450/2520 = 756 + 2450/2520 = 3206/2520
3206/2520 simplified gives 229/180
So, 21/70 + 70/72 = 229/180
In mixed form: 149/180

MathStep (Works offline)

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