Answers

Subtract 40/42 from 15/80

15/80 - 40/42 is -257/336.

Steps for subtracting fractions

1. Find the least common denominator or LCM of the two denominators:
   LCM of 80 and 42 is 1680
   
   Next, find the equivalent fraction of both fractional numbers with denominator 1680
2. For the 1st fraction, since 80 × 21 = 1680,
   15/80 = 15 × 21/80 × 21 = 315/1680
3. Likewise, for the 2nd fraction, since 42 × 40 = 1680,
   40/42 = 40 × 40/42 × 40 = 1600/1680
4. Subtract the two like fractions:
   315/1680 - 1600/1680 = 315 - 1600/1680 = -1285/1680
5. After reducing the fraction, the answer is -257/336

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