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A quick method for mutliplying by 11 (number tricks, math cheats)

Updated on January 6, 2013

In this hub, I will show you a quick way to multiply any two digit number by 11. There are 2 different situations so be careful!

Method 1

This is for 2 digit numbers where the sum of the digits is less than or equal to 9:

Step 1 Find the sum of the two digits of the number that is being multiplied by 11.

Step 2 Put this digit between the two digits of the number that is being multiplied by 11. This is your answer.

Method 2

This is for 2 digit numbers where the sum of the digits is more than 9:

Step 1 Find the sum of the two digits of the number that is being multiplied by 11.

Step 2 Put the last digit from your answer from step 1 between the two digits of the number that is being multiplied by 11 and add 1 onto the first digit of this new number. This is your answer.

Let’s take a look at some examples:

Example 1

Use one of the methods above to work out 26 × 11.

2 + 6 = 8, so apply method 1 as the sum is less than or equal to 9.

Just put 8 between the numbers 2 and 6 to give 286.

Example 2

Use one of the methods above to work out 72 × 11.

7 + 2 = 9, so apply method 1 as the sum is less than or equal to 9.

Just put 9 between the numbers 7 and 2 to give 792.

Example 3

Use one of the methods above to work out 32 × 11.

3 + 2 = 5, so apply method 1 as the sum is less than or equal to 9.

Just put 5 between the numbers 3 and 2 to give 352.

Example 4

Use one of the methods above to work out 85 × 11.

8 + 5 = 13, so apply method 2 as the sum is more than 9.

Put 3 between the numbers 8 and 5 to give 835 and now add 1 to the first digit to give 935.

Example 5

Use one of the methods above to work out 98 × 11.

9 + 8 = 17, so apply method 2 as the sum is more than 9.

Put 7 between the numbers 9 and 8 to give 978 and now add 1 to the first digit to give 1078.

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