Add 21/18 and 15/42, Solve 1 3/18 + 15/42 as a fraction

Add 21/18 and 15/42

1^st number: 1 3/18, 2^nd number: 15/42

21/18 + 15/42 is 32/21.

Find the least common denominator or LCM of the two denominators:
LCM of 18 and 42 is 126

Next, find the equivalent fraction of both fractional numbers with denominator 126
For the 1st fraction, since 18 × 7 = 126,
21/18 = 21 × 7/18 × 7 = 147/126
Likewise, for the 2nd fraction, since 42 × 3 = 126,
15/42 = 15 × 3/42 × 3 = 45/126
Add the two like fractions:
147/126 + 45/126 = 147 + 45/126 = 192/126
192/126 simplified gives 32/21
So, 21/18 + 15/42 = 32/21
In mixed form: 111/21

MathStep (Works offline)

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