Subtract 90/54 from 20/21, Solve 20/21

Subtract 90/54 from 20/21

1^st number: 20/21, 2^nd number: 1 36/54

20/21 - 90/54 is -5/7.

Find the least common denominator or LCM of the two denominators:
LCM of 21 and 54 is 378

Next, find the equivalent fraction of both fractional numbers with denominator 378
For the 1st fraction, since 21 × 18 = 378,
20/21 = 20 × 18/21 × 18 = 360/378
Likewise, for the 2nd fraction, since 54 × 7 = 378,
90/54 = 90 × 7/54 × 7 = 630/378
Subtract the two like fractions:
360/378 - 630/378 = 360 - 630/378 = -270/378
After reducing the fraction, the answer is -5/7

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