MULTIPLYING NUMBERS BY 11

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If you were asked to multiply a given number by 11, how would you do it? I’m sure you’ll do the normal multiplication process like this:

                          23

                x    11                                             

                      23

                   23   

                   253

Did you know that there is a simple way of multiplying a number by 11? You can multiply the numbers in a few second! 

Let us use the previous example: (23)(11)

                             23

                    2                 3                          copy the digits of the number

                       2+3 = 5                               add the digits

                         253                                    5 is written between 2 and 3

Therefore, (23)(11) = 253.

Let us have another example: (56)(11) = ?

                             56

     5                 6                          copy the digits of the number

                     5+6 = 11                               add the digits

              (5+1)    1       6                            since the result is a two digit number, retain the 

                                                                           ones digit and add the tens digit to 5

                    6      1       6

Therefore, (56)(11) = 616.

It is that easy! Now, it is your turn. Find the product of each pair of numbers.

1.      (34)(11)

2.     (45)(11)

3.     (67)(11)

4.    (85)(11)

5.     (98)(11)

Answers:

    1. 374

    2. 495

    3. 737

    4. 935

    5. 1,078

   

Posted in: Math Applications,Math Appreciation,Math Patterns