MemoryMentor’s Blog

How do we multiply by eleven easily?

First we will try this by writing the answer backwards.

So, when always multiplying a large number by 11, the last number will always be the last number of the sum we are multiplying.

Let me explain.

176 is the number we are multiplying.

So the last number in out answer will be 6. If the sum was 143 the last number in our answer would be 3… get it?

So now what?

Easy, just add the next number to the last number, 7 + 6 = 13

So the next last number will be 3, carry the 1.

Add the 7 and 1 together, giving 8, then add the carried 1, 9 then write that number as our next part of the answer, 936

Then, the last number will be the first number in our sum, in this case 1.

So the answer is 1936.

Try 278Last number is 8

7 + 8 = 15

Second last number is 5, carry the 1

7 + 2 = 9 add the carried 1, 10

Third last number is 0, carry the 1

Add the carried 1 to the first number in the sum, 2 giving:

2 + 1 = 3

So the answer is 3058!

Alternatively, you could always just add a zero to the number you are multiplying and then add the original number to it again…

156 X 11

try it this way:

Add a zero to the end

1560

Add 156 to this

1560 + 156 = 1716

Whatever method works best, stick to it!