Subtract 90/27 from 72/21, Solve 3 9/21

Subtract 90/27 from 72/21

1^st number: 3 9/21, 2^nd number: 3 9/27

72/21 - 90/27 is 2/21.

Find the least common denominator or LCM of the two denominators:
LCM of 21 and 27 is 189

Next, find the equivalent fraction of both fractional numbers with denominator 189
For the 1st fraction, since 21 × 9 = 189,
72/21 = 72 × 9/21 × 9 = 648/189
Likewise, for the 2nd fraction, since 27 × 7 = 189,
90/27 = 90 × 7/27 × 7 = 630/189
Subtract the two like fractions:
648/189 - 630/189 = 648 - 630/189 = 18/189
After reducing the fraction, the answer is 2/21

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