Subtract 90/72 from 72/21, Solve 3 9/21

Subtract 90/72 from 72/21

1^st number: 3 9/21, 2^nd number: 1 18/72

72/21 - 90/72 is 61/28.

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,
72/21 = 72 × 24/21 × 24 = 1728/504
Likewise, for the 2nd fraction, since 72 × 7 = 504,
90/72 = 90 × 7/72 × 7 = 630/504
Subtract the two like fractions:
1728/504 - 630/504 = 1728 - 630/504 = 1098/504
After reducing the fraction, the answer is 61/28
In mixed form: 25/28

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