Methods for doubling and halving

Doubling is the same as multiplying by 2, so any method that works for multiplying by 2 also works for doubling. The same is true for halving and dividing by 2.

1. Use objects or fingers to help.

2. Use knowledge of 2 times table

3. Write down the number. Split it into tens and ones. Double or halve each part then add the answers back together.

Eg. doubling

Remember to separate the tens and ones to 30 and 4, not 3 and 4!

This method can also be used for halving.

If it is difficult to halve the tens, separate the tens into a 10 and the rest of the tens.

eg. halving

Doubling

This week in maths we have been doubling and halving. This website has a doubling function machine where you can put in any number and have to work it the double before the machine does: http://ngfl.northumberland.gov.uk/maths/num%20machine/double.html

Another website that uses doubling and halving strategies to reach a given target number:
http://www.crickweb.co.uk/assets/resources/flash.php?&file=crazyc

An easier doubling game:
http://www.ictgames.com/rhoodbeyond10.html

A great website for doubling numbers up to 100. The number is presented using place value cards showing the number made up of 10s and 1s. There are also abacuses at the top of the screen showing two lots of 10s and 1s. These can be counted to help calculate the double:
http://www.ictgames.com/woodcards.html