Multiplication of two number in between 90 - 100.


Multiplication of two numbers less than 100.

Condition:

Both of the numbers must be less than 100. Preferably the two numbers are not less than 88. For numbers less than 88, it will be a little bit challenging to calculate it mentally.

Example 1:
97 x 94 = ?

Steps:

  1. Find the 100's complement of the two numbers. For example, 97 is 3 less than 100, hence we put its complement as -3, and with the same method, the complement of 94 is -6.
  2. We add the multiplicand to the complement of the multiplier or add the multiplier to the complement of the multiplicand. (You should always get the same answer for both.) The answer obtained will be the last two digits of the product.
  3. Find the product of the two complement numbers (in this case, -3 and -6). This will be the first two digits of the product.
  4. And we get the answer. 97 x 94 = 9118
Explanation:
97 x 94
= 97 x (100 - 6)
= (97 x 100) - (97 x 6)
= (97 x 100) - [(100 - 3) x 6]
= (97 x 100) - (6 x 100) + (3 x 6)
= (97 - 6)•100 + (3 x 6)

Example 2:
95 x 98 = ?
100's complement of the two numbers:
95 → -5
98 → -2

95 - 2 = 93

Product of the complements:
(-5) x (-2) = 10

95 x 98 = 9310

Example 3:
96 x 99 = ?

100's complement of the two numbers:
96 → -4
99 → -1

Product of the complements:
96 - 1 = 95
(-4) x (-1) = 4

96 x 99 = 9504

Take note that, if the product of the complement is a single digit number, we make it double digit by adding a 0 in front of the number. For example, 4 become 04.

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