3. Trick - Multiplication

Today we will learn about multiplication... once again, the same trick but with a difference.

The trick that I will tell you now will give you more power. After this, you will never need to know any table more than 5x5. I call this extension as "10's complement".

10's complement of any digit x is 10 - x. In two numbers that you are multiplying, take 10's complement of any digit greater than 5 and increase the digit next to it (higher significant value) by one. Reverse this process while calculating final value. The digits whose complements are taken shall be called "barred".

Calculation with barred digits will be considered as being done with negative numbers. For example, bar-4 * 4 = bar-16 and bar-8 + 3 = bar-5.

Now, I shall demonstrate it with an example:

    478*129 = 522*131

    522
   x131
 --------
   53342
   11
 --------

  = 62342 = 61662