Subtract 20/90 from 15/21, Solve 15/21

Subtract 20/90 from 15/21

15/21 - 20/90 is 31/63.

Find the least common denominator or LCM of the two denominators:
LCM of 21 and 90 is 630

Next, find the equivalent fraction of both fractional numbers with denominator 630
For the 1st fraction, since 21 × 30 = 630,
15/21 = 15 × 30/21 × 30 = 450/630
Likewise, for the 2nd fraction, since 90 × 7 = 630,
20/90 = 20 × 7/90 × 7 = 140/630
Subtract the two like fractions:
450/630 - 140/630 = 450 - 140/630 = 310/630
After reducing the fraction, the answer is 31/63

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