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

Subtract 15/20 from 21/90

21/90 - 15/20 is -31/60.

Find the least common denominator or LCM of the two denominators:
LCM of 90 and 20 is 180

Next, find the equivalent fraction of both fractional numbers with denominator 180
For the 1st fraction, since 90 × 2 = 180,
21/90 = 21 × 2/90 × 2 = 42/180
Likewise, for the 2nd fraction, since 20 × 9 = 180,
15/20 = 15 × 9/20 × 9 = 135/180
Subtract the two like fractions:
42/180 - 135/180 = 42 - 135/180 = -93/180
After reducing the fraction, the answer is -31/60

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