Subtract 42/40 from 20/21, Solve 20/21

Subtract 42/40 from 20/21

1^st number: 20/21, 2^nd number: 1 2/40

20/21 - 42/40 is -41/420.

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,
20/21 = 20 × 40/21 × 40 = 800/840
Likewise, for the 2nd fraction, since 40 × 21 = 840,
42/40 = 42 × 21/40 × 21 = 882/840
Subtract the two like fractions:
800/840 - 882/840 = 800 - 882/840 = -82/840
After reducing the fraction, the answer is -41/420

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