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Subtract 30/40 from 12/42

12/42 - 30/40 is -13/28.

Steps for subtracting fractions

  1. Find the least common denominator or LCM of the two denominators:
    LCM of 42 and 40 is 840

    Next, find the equivalent fraction of both fractional numbers with denominator 840
  2. For the 1st fraction, since 42 × 20 = 840,
    12/42 = 12 × 20/42 × 20 = 240/840
  3. Likewise, for the 2nd fraction, since 40 × 21 = 840,
    30/40 = 30 × 21/40 × 21 = 630/840
  4. Subtract the two like fractions:
    240/840 - 630/840 = 240 - 630/840 = -390/840
  5. After reducing the fraction, the answer is -13/28

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