Subtract 21/12 from 42/80, Solve 42/80

Subtract 21/12 from 42/80

1^st number: 42/80, 2^nd number: 1 9/12

42/80 - 21/12 is -49/40.

Find the least common denominator or LCM of the two denominators:
LCM of 80 and 12 is 240

Next, find the equivalent fraction of both fractional numbers with denominator 240
For the 1st fraction, since 80 × 3 = 240,
42/80 = 42 × 3/80 × 3 = 126/240
Likewise, for the 2nd fraction, since 12 × 20 = 240,
21/12 = 21 × 20/12 × 20 = 420/240
Subtract the two like fractions:
126/240 - 420/240 = 126 - 420/240 = -294/240
After reducing the fraction, the answer is -49/40

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