Subtract 80/90 from 21/84, Solve 21/84

Subtract 80/90 from 21/84

21/84 - 80/90 is -23/36.

Find the least common denominator or LCM of the two denominators:
LCM of 84 and 90 is 1260

Next, find the equivalent fraction of both fractional numbers with denominator 1260
For the 1st fraction, since 84 × 15 = 1260,
21/84 = 21 × 15/84 × 15 = 315/1260
Likewise, for the 2nd fraction, since 90 × 14 = 1260,
80/90 = 80 × 14/90 × 14 = 1120/1260
Subtract the two like fractions:
315/1260 - 1120/1260 = 315 - 1120/1260 = -805/1260
After reducing the fraction, the answer is -23/36

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