Subtract 42/72 from 4/21, Solve 4/21

Subtract 42/72 from 4/21

4/21 - 42/72 is -11/28.

Find the least common denominator or LCM of the two denominators:
LCM of 21 and 72 is 504

Next, find the equivalent fraction of both fractional numbers with denominator 504
For the 1st fraction, since 21 × 24 = 504,
4/21 = 4 × 24/21 × 24 = 96/504
Likewise, for the 2nd fraction, since 72 × 7 = 504,
42/72 = 42 × 7/72 × 7 = 294/504
Subtract the two like fractions:
96/504 - 294/504 = 96 - 294/504 = -198/504
After reducing the fraction, the answer is -11/28

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