Multiply by 21, Another method

As I promised you in my previous article, another method of multiplying by 21

Rule is Prev. digit + twice of next digit ( Carry over if required )

Let us take an example  456 X 21

Apply the rule from left to right

0 + 2 X 4   = 8 ( Since there is no previous digit for four, we added zero )

4 + 2 X 5 = 14

5 + 2 X 6 = 17 

The last digit is same as the last digit in the problem ( 456 ), so it is 6.

Let us write it together.

8 |  14 | 17 | 6, we have to apply carry over.

     

              So the answer is :   9576

Check the answer with your calculator, soon you may not need that.

This method can be applied for any number, however big it is !!!!!!

Enjoy doing maths !!!!!

Please Note : | symbol is used here as partition, no other special meaning.