For those that love math and how numbers are manipulated using mathematical
operations, this article is for you. For those that want to improve
their mental math skills, this article is for you as well. Even those
that don't like math can benefit from learning how to do mental math.
There are many types of problems one can do mentally, but for the scope
of this article, I will concentrate on the simple problem of multiplying
any two-digit number by 11.

As a math tutor for 14 years, I have taught
several students this method in attempts to transition from the use of a
calculator for all problems to performing more calculations in the
head.

Let's take a simple example, multiplying 34 by 11. To solve
the problem, simply add the digits 3 + 4 = 7 and write the digits
between the 3 and the 4. Your answer is 374. Very simply done. You can
check your answer by multiplying by hand or using a calculator. Let's
take another example, 42 times 11. Add the 4 +2 = 6 and write 6 between
the 4 and 2. The answer is 462. Now that was easy, but don't get overly
excited just yet. There are other cases where a little more needs to be
done.

For example, suppose the problem is 67 times 11. Although 6
+ 7 = 13, the answer is not 6,137. As before the 3 goes in between the
numbers, but the 1 needs to be added to the 6 to get 7. The correct
answer is 737. Basically think of adding the 1 to the 6 as "carrying"
the 1 like you would in a simple problem such as 13 + 8, add the 3 and 8
to get 11, write down the 1 and carry the 1, adding it to the other 1
to get 21. Let's try another example, suppose the problem is 84 times
11. Add 8 and 4 to get 12. Write the 2 in between the 8 and 4 but
remember to carry the 1, adding to the 8 to get 924. See how easy that
is?

This is just one of several articles I plan to write on
mental math. Others will include mental addition and subtraction, basic
multiplication, mental division, estimations and advanced
multiplication. In the meantime, practice the mental math you learned in
this article. It will exercise your mind and impress your friends!

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