Subtract 21/20 from 18/72, Solve 18/72

Subtract 21/20 from 18/72

1^st number: 18/72, 2^nd number: 1 1/20

18/72 - 21/20 is -4/5.

Find the least common denominator or LCM of the two denominators:
LCM of 72 and 20 is 360

Next, find the equivalent fraction of both fractional numbers with denominator 360
For the 1st fraction, since 72 × 5 = 360,
18/72 = 18 × 5/72 × 5 = 90/360
Likewise, for the 2nd fraction, since 20 × 18 = 360,
21/20 = 21 × 18/20 × 18 = 378/360
Subtract the two like fractions:
90/360 - 378/360 = 90 - 378/360 = -288/360
After reducing the fraction, the answer is -4/5

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