The Clara James Approach to learning

Multiplying 11 by double digits

Dawn Strachan

A few weeks ago, I was working with a lad, he’s brilliant, he’s just finished his GCSEs. We had just a couple of minutes left of the lesson, so we decided on a game of times-tables-noughts-and-crosses.

I pulled up the grid and asked what he’d like to multiply by. He answered 11.

Considering he was doing the higher paper I agreed but thought I’d ‘be clever’ and make the numbers in the grid double digits to make it harder.

But he was still answering them within a flash.

I asked if he was using a calculator and his mum, whom I hadn’t realised was also there, said he was just using a trick that he had learned.

This was eye-opening to me, so I thought I’d share it with you too:

 

Multiplying single digits by 11 is simple.

The digit you are multiplying by 11 is written down twice instead of once:

11x3 = 33

11x8 =88

 

And this apparently is how you multiply 11 by a double digit easily:

Simply add the 2 numbers you are multiplying by 11 together:

12x11

(1+2 = 3) and slide the answer (3) between the number you were multiplying 11 by: 132

 

16x11

1+6 =7

Split the 16 and put 7 in the middle

16x11 =176

 

Another example:

32x11

3+2=5

Split the 32 and place the 5 in the middle:

352