Subtract 42/18 from 40/21, Solve 1 19/21

Subtract 42/18 from 40/21

1^st number: 1 19/21, 2^nd number: 2 6/18

40/21 - 42/18 is -3/7.

Find the least common denominator or LCM of the two denominators:
LCM of 21 and 18 is 126

Next, find the equivalent fraction of both fractional numbers with denominator 126
For the 1st fraction, since 21 × 6 = 126,
40/21 = 40 × 6/21 × 6 = 240/126
Likewise, for the 2nd fraction, since 18 × 7 = 126,
42/18 = 42 × 7/18 × 7 = 294/126
Subtract the two like fractions:
240/126 - 294/126 = 240 - 294/126 = -54/126
After reducing the fraction, the answer is -3/7

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