# 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:

- Short Multiplication - the written method we all learned at school - here's a video to remind you
- The Grid Method as discussed in this article
- 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 )
- 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*.