Add 21/42 and 81/90
21/42 + 81/90 is 7/5.
Steps for adding fractions
- Find the least common denominator or LCM of the two denominators:
LCM of 42 and 90 is 630
Next, find the equivalent fraction of both fractional numbers with denominator 630 - For the 1st fraction, since 42 × 15 = 630,
21/42 = 21 × 15/42 × 15 = 315/630 - Likewise, for the 2nd fraction, since 90 × 7 = 630,
81/90 = 81 × 7/90 × 7 = 567/630 - Add the two like fractions:
315/630 + 567/630 = 315 + 567/630 = 882/630 - 882/630 simplified gives 7/5
- So, 21/42 + 81/90 = 7/5
In mixed form: 12/5
MathStep (Works offline)
Download our mobile app and learn to work with fractions in your own time:
Android and iPhone/ iPad
Related: 21/84+81/90 63/42+81/90