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Subtract 18/21 from 9/20

9/20 - 18/21 is -57/140.

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,
    9/20 = 9 × 21/20 × 21 = 189/420
  3. Likewise, for the 2nd fraction, since 21 × 20 = 420,
    18/21 = 18 × 20/21 × 20 = 360/420
  4. Subtract the two fractions:
    189/420 - 360/420 = 189 - 360/420 = -171/420
  5. After reducing the fraction, the answer is -57/140

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