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Multiplying A Repeating 1s Number By 18

Multiplying A Repeating 1s Number By 18

Multiplying a repeating 1's number by 18

  1. Choose a repeating 1's number (111, etc.)
  2. Multiply it by 18
  3. The product is:
    - first digit is 1
    - next digits are 9's - one fewer than repeating 1's in the original number
    - last digit is 8.
   Example:
  1. If the first number is 11111:
  2. Multiply by 18. The product is:
    first digit is 1: 1
    next digits are 9's, one fewer than 1's: 88888
    last digit is 8: 8
  3. So 11111 × 18 = 199998.

   See the pattern?

  1. If the first number is 111111111:
  2. Multiply by 18. The product is:
    first digit is 1: 1
    next digits are 9's, one fewer than 1's: B 99999999
    last digit is 8: 8
  3. So 1111111111 × 18 = 1999999998.
Follow these three steps and you will be able to give these sometimes large products with ease. Your friend's calculator will not be able to handle these large ones.




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17 Feb, 2020, 10:01:32 AM