Multiplication - the half and double method

Multiplication - the half and double method

Learning maths at primary school age is a little bit like collecting tools for a tool kit. 

Here's a super-useful tool that can come in handy to simplify some tricky looking multiplication.

Multiplying using the half and double method

When you're faced with a multiplication like:

4 x 16 = ?

You have a number of methods to use:

  1. Short Multiplication  - the written method we all learned at school - here's a video to remind you

  2. The Grid Method as discussed in this article

  3. The Distributive Law - which sounds scary but basically means "splitting" it into two easy multiplications - so 4 x 16 becomes (4 x 10 ) + (4 x 6 )

  4. Or sometimes, such as in this example, it's just perfect for the half and double method

Using the half and double method, we can halve one side of the multiplication as long as we double the other - and the answer remains the same.

So,

4 x 16 

becomes:

8 x 8 = 64


Here is another example which looks a little tricky at first:

34 x 5 = ?

But after using the half and double method it becomes:

17 x 10 = 170


The method also works very well with some fractions like this:

3½  x 12 = ?

Doubling removes the fraction so it becomes:

3½  x 12 =  7 x 6 = 42


Likewise with decimals:

4.5  x 8   =  9 x 4  = 36

 

The key to using the half and double strategy is choosing when it makes the problem easier. Here is a guide:

  • Is one of the sides 5? If so doubling will give 10 which is easy.
  • Is the side I need to halve even?
  • Does one side include a half or 0.5? If so doubling will remove it.

And that's it. A handy little multiplication strategy to add to your "maths toolkit." 

 

I'm Ged, Co-founder of Komodo, ex-maths teacher and dad. If you have any questions please get in touch.

About Komodo – Komodo is a fun and effective way to boost primary maths skills. Designed for 5 to 11-year-olds to use in the home, Komodo uses a little and often approach to learning maths (15 minutes, three to five times per week) that fits into the busy routine. Komodo users develop fluency and confidence in maths – without keeping them at the screen for long.

Find out more about Komodo and how it helps thousands of children each year do better at maths - you can even try Komodo for free.

Related Posts

Summer learning tips (that won't spoil your kids' summer)

Kids need to wind down, relax and have fun over the summer but also be prepared for the return to school in September. Find out how this busy mum walks the fine balance between summer fun and maintaining her kids learning level.

Introducing the new Komodo belt journey - here's how to update your app

The Komodo team have been busy working away behind the scenes on our latest version of Komodo and can now reveal the new Komodo belt journey - an extra reward for all our hard-working learners.