Subtract 18/90 from 20/21, Solve 20/21

Subtract 18/90 from 20/21

20/21 - 18/90 is 79/105.

Find the least common denominator or LCM of the two denominators:
LCM of 21 and 90 is 630

Next, find the equivalent fraction of both fractional numbers with denominator 630
For the 1st fraction, since 21 × 30 = 630,
20/21 = 20 × 30/21 × 30 = 600/630
Likewise, for the 2nd fraction, since 90 × 7 = 630,
18/90 = 18 × 7/90 × 7 = 126/630
Subtract the two like fractions:
600/630 - 126/630 = 600 - 126/630 = 474/630
After reducing the fraction, the answer is 79/105

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