# Multiplication - the Halving and Doubling Strategy

Learning math at elementary school age is a little bit like collecting tools for a tool kit.

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

## Multiplying using the halving and doubling strategy

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 learnt 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 halving and doubling 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 halving and doubling 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 'math toolkit'.

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

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