Add 72/21 and 80/72, Solve 3 9/21 + 1 8/72 as a fraction

Add 72/21 and 80/72

1^st number: 3 9/21, 2^nd number: 1 8/72

72/21 + 80/72 is 286/63.

Find the least common denominator or LCM of the two denominators:
LCM of 21 and 72 is 504

Next, find the equivalent fraction of both fractional numbers with denominator 504
For the 1st fraction, since 21 × 24 = 504,
72/21 = 72 × 24/21 × 24 = 1728/504
Likewise, for the 2nd fraction, since 72 × 7 = 504,
80/72 = 80 × 7/72 × 7 = 560/504
Add the two like fractions:
1728/504 + 560/504 = 1728 + 560/504 = 2288/504
2288/504 simplified gives 286/63
So, 72/21 + 80/72 = 286/63
In mixed form: 434/63

MathStep (Works offline)

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