Mathematricks

By Hannah McDowell Friday, April 18, 2014

Each week, we’ll be giving you a dose of mathematricks to show you the tricks behind the maths.

Today we’ll start with our quick and easy trick to understand the 11 times tables.

Our 11 Times Trick

Multiplying by ten is easy – just add zero, but what about the 11 times table? Here’s our easy trick to give you the same confidence in 11 times tables as you have with multiples of ten.

The Mathematrick

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Take the original number and imagine a space between the two digits (for this example we’ll use 41)

4_1

Next add these two numbers together and put them in the space you have created:

4(4+1)1

That is it – you have the answer: 451.

It’s a little more complicated when this middle number is 2 digits, but follow the trick carefully and you’ll get the hang of it.

So, if the numbers in the middle add up to a 2 digit number, just insert the second number and then add 1 to the first.

Let’s take 75 x 11 as an example.

*7(7+5)5 = 7(12)5 *

Insert the second number (2) in the space you have created.

7 (2) 5.

Now add 1 to the first number (7+1)

Then, we have our answer, 825.

Works every time!

If you’d like to know more mathematricks, check out our Mathematricks page.