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Subtract 18/20 from 21/28

21/28 - 18/20 is -3/20.

Steps for subtracting fractions

  1. Find the least common denominator or LCM of the two denominators:
    LCM of 28 and 20 is 140

    Next, find the equivalent fraction of both fractional numbers with denominator 140
  2. For the 1st fraction, since 28 × 5 = 140,
    21/28 = 21 × 5/28 × 5 = 105/140
  3. Likewise, for the 2nd fraction, since 20 × 7 = 140,
    18/20 = 18 × 7/20 × 7 = 126/140
  4. Subtract the two like fractions:
    105/140 - 126/140 = 105 - 126/140 = -21/140
  5. After reducing the fraction, the answer is -3/20

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