Subtract 63/40 from 30/21, Solve 1 9/21

Subtract 63/40 from 30/21

1^st number: 1 9/21, 2^nd number: 1 23/40

30/21 - 63/40 is -41/280.

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,
30/21 = 30 × 40/21 × 40 = 1200/840
Likewise, for the 2nd fraction, since 40 × 21 = 840,
63/40 = 63 × 21/40 × 21 = 1323/840
Subtract the two like fractions:
1200/840 - 1323/840 = 1200 - 1323/840 = -123/840
After reducing the fraction, the answer is -41/280

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