Subtract 21/20 from 27/42, Solve 27/42

Subtract 21/20 from 27/42

1^st number: 27/42, 2^nd number: 1 1/20

27/42 - 21/20 is -57/140.

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

Next, find the equivalent fraction of both fractional numbers with denominator 420
For the 1st fraction, since 42 × 10 = 420,
27/42 = 27 × 10/42 × 10 = 270/420
Likewise, for the 2nd fraction, since 20 × 21 = 420,
21/20 = 21 × 21/20 × 21 = 441/420
Subtract the two like fractions:
270/420 - 441/420 = 270 - 441/420 = -171/420
After reducing the fraction, the answer is -57/140

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