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Subtract 20/21 from 15/20

15/20 - 20/21 is -17/84.

Steps for subtracting fractions

  1. Find the least common denominator or LCM of the two denominators:
    LCM of 20 and 21 is 420
  2. For the 1st fraction, since 20 × 21 = 420,
    15/20 = 15 × 21/20 × 21 = 315/420
  3. Likewise, for the 2nd fraction, since 21 × 20 = 420,
    20/21 = 20 × 20/21 × 20 = 400/420
  4. Subtract the two fractions:
    315/420 - 400/420 = 315 - 400/420 = -85/420
  5. After reducing the fraction, the answer is -17/84

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