Tricky Tricks ›› Math Tricks ›› Multiply Tricks ›› Multiplying two digit number by 31

Multiplying two digit number by 31

Multiplying a 2-digit number by 31
  1. Select a 2-digit number.
  2. Multiply it by 3.
  3. Add one zero.
  4. Add the original number.

Example:

  1. The 2-digit number chosen to multiply by 31 is 21.
  2. Multiply by 3: 3 × 21 = 63.
  3. Add one zero: 630.
  4. Add original number: 630 + 21 = 651.
  5. So 31 × 21 = 651.

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