Subtract 72/18 from 5/21, Solve 5/21

Subtract 72/18 from 5/21

1^st number: 5/21, 2^nd number: 4 0/18

5/21 - 72/18 is -79/21.

Find the least common denominator or LCM of the two denominators:
LCM of 21 and 18 is 126

Next, find the equivalent fraction of both fractional numbers with denominator 126
For the 1st fraction, since 21 × 6 = 126,
5/21 = 5 × 6/21 × 6 = 30/126
Likewise, for the 2nd fraction, since 18 × 7 = 126,
72/18 = 72 × 7/18 × 7 = 504/126
Subtract the two like fractions:
30/126 - 504/126 = 30 - 504/126 = -474/126
After reducing the fraction, the answer is -79/21

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