Add 21/28 and 15/8, Solve 21/28 + 1 7/8 as a fraction

Add 21/28 and 15/8

1^st number: 21/28, 2^nd number: 1 7/8

21/28 + 15/8 is 21/8.

Find the least common denominator or LCM of the two denominators:
LCM of 28 and 8 is 56

Next, find the equivalent fraction of both fractional numbers with denominator 56
For the 1st fraction, since 28 × 2 = 56,
21/28 = 21 × 2/28 × 2 = 42/56
Likewise, for the 2nd fraction, since 8 × 7 = 56,
15/8 = 15 × 7/8 × 7 = 105/56
Add the two like fractions:
42/56 + 105/56 = 42 + 105/56 = 147/56
147/56 simplified gives 21/8
So, 21/28 + 15/8 = 21/8
In mixed form: 25/8

MathStep (Works offline)

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