Multiply by 21

Multiply any number by 21 in seconds

Very very simple and convenient method to multiply any number with 21.

Take the example of 45 X 21

First multiply 45 X 20 = 900
           Add 45                   45
                                        ------
                                        945

Take 567 X 21

Step 1 : 567 X 20 = 11340
Step 2 :                 +     567
                                ----------
                                 11907
                                ----------

The same method could be extended for 31, 41, 51.... etc multiplication as long as a child is comfortable in Tables.

However this method will not be effective as the no. of digits in the first number increases ( If a child is comfortable enough, you can use this).

We can use another method which is related to multiplication of 11, will be discussed in next post.