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 8__13__5! 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 9__3__5:

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 3__45__4.

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