Multiplication of any number by a number near 100

It is easy to multiply any number by 100. We just need to append two zeroes to the end of that multiplicand number. For example, 100 x 23 = 2300. But, what if the multiplier is a number that is near to 100, such as 101, or 99?

To multiply a number, a, by a number, b, that is near to 100, here are the steps.

1. Multiply the multiplicand by 100.
   c = 100 x b


2. Subtract 100 from the multiplier.
   d = b - 100


3. Multiply multiplicand, a with the result from step 3, d.
   e = d x a


4. Finally, add the result from steps 1 and 3.

In simple words, we could write it as

( 100 x multiplicand ) + ( (multiplier - 100) x multiplicand )

Example:

1. 101 x 23 = (100 x 23) + ( (101 - 100) x 23 ) = 2300 + (1 x 23) = 2300 + 23 = 2323


2. 99 x 23 = (100 x 23) + ( (99 - 100) x 23 ) = 2300 + (-1 x 23) = 2300 - 23 = 2277

Now, you can try to do it on larger numbers such as 101 x 297, or even slightly larger or smaller than 100 multiplier, such as 103 x 74.