Subtract 20/8 from 15/42, Solve 15/42

Subtract 20/8 from 15/42

1^st number: 15/42, 2^nd number: 2 4/8

15/42 - 20/8 is -15/7.

Find the least common denominator or LCM of the two denominators:
LCM of 42 and 8 is 168

Next, find the equivalent fraction of both fractional numbers with denominator 168
For the 1st fraction, since 42 × 4 = 168,
15/42 = 15 × 4/42 × 4 = 60/168
Likewise, for the 2nd fraction, since 8 × 21 = 168,
20/8 = 20 × 21/8 × 21 = 420/168
Subtract the two like fractions:
60/168 - 420/168 = 60 - 420/168 = -360/168
After reducing the fraction, the answer is -15/7

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