Multiplication of a double digit number by 9. Case #4


There are a few tricks to multiply a double digit number by 9, according to different conditions:
  1. The number is a multiple of 11.
  2. The tens digit is less than the ones digit by one.
  3. The tens digit is less than the ones digit.
  4. The tens digit is greater than the ones digit.
In this page, we are going to discuss about case four, where the number a tens digit is greater than the ones digit. (Example, 42, 85, 62, 93 ....)

Condition:

  1. The multiplicand is a double digit number where the tens digit is greater than the ones digit .
  2. The multiplier is 9.
Example 1
41 x 9 = ?
  1. Deduct the multiplicand by 10, and then multiply the answer by 10. In this case, 41 - 10 = 31. 31 x 10 = 310.
  2. Find the 100's complement of the multiplicand. In this case, 100 - 41 = 59. Sum up the answer obtained in step 1 and 2.

Example 2
96 x 9 = ?
  1. (96 - 10) x 100 = 860
  2. 100 - 96 = 4
Therefore, 96 x 9 = 860 + 4 = 864

Example 3
62 x 9 = ?
  1. (62 - 10) x 100 = 520
  2. 100 - 62 = 38
Therefore, 62 x 9 = 520 + 38 = 558

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