Add 21/42 and 18/5, Solve 21/42 + 3 3/5 as a fraction

Add 21/42 and 18/5

1^st number: 21/42, 2^nd number: 3 3/5

21/42 + 18/5 is 41/10.

Find the least common denominator or LCM of the two denominators:
LCM of 42 and 5 is 210

Next, find the equivalent fraction of both fractional numbers with denominator 210
For the 1st fraction, since 42 × 5 = 210,
21/42 = 21 × 5/42 × 5 = 105/210
Likewise, for the 2nd fraction, since 5 × 42 = 210,
18/5 = 18 × 42/5 × 42 = 756/210
Add the two like fractions:
105/210 + 756/210 = 105 + 756/210 = 861/210
861/210 simplified gives 41/10
So, 21/42 + 18/5 = 41/10
In mixed form: 41/10

MathStep (Works offline)

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