Subtract 42/90 from 20/21, Solve 20/21

Subtract 42/90 from 20/21

20/21 - 42/90 is 17/35.

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,
42/90 = 42 × 7/90 × 7 = 294/630
Subtract the two like fractions:
600/630 - 294/630 = 600 - 294/630 = 306/630
After reducing the fraction, the answer is 17/35

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