Multiplying any two digit number by eleven is easier than most people think!  Would you like to be able to calculate a math problem like this quickly in your head?  Here is how to do it easily, mentally, and faster than you can enter it into a calculator!

 

Consider this Problem:

 

32 X 11

 

To solve this problem, simply add the digits 3 + 2 = 5, then put the 5 between the 3 and the 2, and there is your answer, 352.

 

Try another one:

 

53 x 11

 

Since 5 + 3 = 8, your answer is simply

 

583

 

NOW DON’T GET TOO EXCITED!  Suppose the problem is 85 X 11?  Even though 8 + 5 = 13, the answer is NOT 8135!  As before, the 3 goes in between the numbers, but the 1 needs to be added to the 8 to get the correct answer of 935:

 

Think of it this way:

 

1

835

935

 

Here is another example:  Try 57 x 11.

Since 5 + 7 = 12, the answer would be:

 

1

527

627

 

Now try this one as fast as you can: 77 x 11.

 

If you got the answer 847, then give yourself a high five!  Now if you tell a friend or teacher that you can multiply, in your head, any two digit number by 11 it won’t be long before they ask you to do 99 x 11.  Can you answer them?

 

1

989

1089

 

Now if you are wondering if this method can be used for 3 or 4 digit (or larger) numbers by eleven, then wonder no more because it is!

 

If you have a problem like 314 x 11, the answer still begins with 3 and ends with 4.  Since 3 + 1 = 4, and 1 + 4 = 5, the answer will be 3454.

 

I’ll blog more on the larger numbers at a different time, but for now, enjoy the new way of dazzling your friends and teachers with your new found, simple way to Math!

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Trevor.

 

 

 

Source:

Secrets of Mental Math