Add 80/21 and 15/42, Solve 3 17/21 + 15/42 as a fraction

Add 80/21 and 15/42

1^st number: 3 17/21, 2^nd number: 15/42

80/21 + 15/42 is 25/6.

Find the least common denominator or LCM of the two denominators:
LCM of 21 and 42 is 42

Next, find the equivalent fraction of both fractional numbers with denominator 42
For the 1st fraction, since 21 × 2 = 42,
80/21 = 80 × 2/21 × 2 = 160/42
Likewise, for the 2nd fraction, since 42 × 1 = 42,
15/42 = 15 × 1/42 × 1 = 15/42
Add the two like fractions:
160/42 + 15/42 = 160 + 15/42 = 175/42
175/42 simplified gives 25/6
So, 80/21 + 15/42 = 25/6
In mixed form: 41/6

MathStep (Works offline)

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