Subtract 90/40 from 7/21, Solve 7/21

Subtract 90/40 from 7/21

1^st number: 7/21, 2^nd number: 2 10/40

7/21 - 90/40 is -23/12.

Find the least common denominator or LCM of the two denominators:
LCM of 21 and 40 is 840

Next, find the equivalent fraction of both fractional numbers with denominator 840
For the 1st fraction, since 21 × 40 = 840,
7/21 = 7 × 40/21 × 40 = 280/840
Likewise, for the 2nd fraction, since 40 × 21 = 840,
90/40 = 90 × 21/40 × 21 = 1890/840
Subtract the two like fractions:
280/840 - 1890/840 = 280 - 1890/840 = -1610/840
After reducing the fraction, the answer is -23/12

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