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Weighted Mean Circle Geometry, Number Pi Money Polynomial Factoring Combinations without Repetition Sine Rule Addition SumsWhen it comes to multiplication sums, multiplication by  11 can be quite an interesting
subject all on its own.

When multiplying  11 by whole numbers, there is often a pattern that appears, which can
make future multiplication sums by  11 quicker and easier.

Multiplying a single digit number by  11, conveniently results in a  2 digit
number.

With the pattern that the result is the same original single digit appearing twice.

With larger numbers multiplied by **11**, there is also a pattern that can be observed.

Below are two examples of multiplication sums involving  11 using long multiplication.

Both multiplications result in an answer that is a  3 digit number.

Something that happened in both cases, was that the original digits from the number being multiplied
by  11 in the sum, also appeared in the answer.

Along with the middle digit of the answer being the result of an addition of the  2
original digits.

Knowing this, can help make multiplying a  2 digit number by  11 quicker whenever it's required.

Sometimes though, the digits of a 2 digit number can add up to a number that is greater than  9.

Such as if you have the sum **67** × **11**.

Now **6** + **7** = **13**,

if we just followed straight away with the approach from before without doing
anything differently, we would have:

This however, is the wrong answer to the multiplication sum.

What we want to do with the **13**, is to carry the **1** over to the left and add on.

This is the extra step we need to do to get the correct answer.

The approaches to dealing with multiplication by 11 shown on this page can make doing certain multiplication sums a bit quicker.

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