Subtract 72/42 from 15/20, Solve 15/20

Subtract 72/42 from 15/20

1^st number: 15/20, 2^nd number: 1 30/42

15/20 - 72/42 is -27/28.

Find the least common denominator or LCM of the two denominators:
LCM of 20 and 42 is 420

Next, find the equivalent fraction of both fractional numbers with denominator 420
For the 1st fraction, since 20 × 21 = 420,
15/20 = 15 × 21/20 × 21 = 315/420
Likewise, for the 2nd fraction, since 42 × 10 = 420,
72/42 = 72 × 10/42 × 10 = 720/420
Subtract the two like fractions:
315/420 - 720/420 = 315 - 720/420 = -405/420
After reducing the fraction, the answer is -27/28

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