Subtract 21/42 from 12/40
12/40 - 21/42 is -1/5.
Steps for subtracting fractions
- Find the least common denominator or LCM of the two denominators:
LCM of 40 and 42 is 840
Next, find the equivalent fraction of both fractional numbers with denominator 840 - For the 1st fraction, since 40 × 21 = 840,
12/40 = 12 × 21/40 × 21 = 252/840 - Likewise, for the 2nd fraction, since 42 × 20 = 840,
21/42 = 21 × 20/42 × 20 = 420/840 - Subtract the two like fractions:
252/840 - 420/840 = 252 - 420/840 = -168/840 - After reducing the fraction, the answer is -1/5
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