Multiplication of a double digit number by 9. Case #3



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 three, where the number a tens digit is less than the ones digit.

Condition:

  1. The multiplicand is a double digit number where the tens digit is less than the ones digit .
  2. The multiplier is 9.
Example 1
26 x 9 = ?
  1. Let's say the answer is x. x must be a 3 digits number. The tens digit of the multiplicand will be the last digit of x.
  2. Multiply the first digit of the multiplicand by 9. In this case, 6 x 9 = 54. The first digit of the product will be the first digit of x (see image below.)
  3. Lastly, deduct the first digit of the multiplicand from the first digit of the product we obtained in step 2, and put it as the second digit of x. (see image below)
Example 2
37 x 9 = ?

  1. 37 x 9 = 3 __ __
  2. 7 x 9 = 63
  3. 6 - 3 = 3

Therefore, 37 x 9 = 333

Example 3
48 x 9 = ?
  1. 48 x 9 = 4 __ __
  2. 8 x 9 = 72
  3. 7 - 4 = 3
Therefore, 48 x 9 = 432

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