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  1. Multiplication
  2. Division
  3. Subtraction
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This is one of my favorite.

Condition:
Subtraction of two double digits number where the first and second digit of the first number equal to the second and first digit of the second number.

Example:

Method:


For the minuend, tens digit subtract by the ones digit and then multiply by 9.

Example:

85 - 58 = (8 - 5) x 9 = 27
64 - 46 = (6 - 4) x 9 = 18
71 - 17 = (7 - 1) x 9 = 54
91 - 19 = (9 - 1) x 9 = 72