Year 4

We can double two-digit numbers

Year 4 Unit 7a

What we are learning:

• When we double we make a number twice as big. We multiply it by 2.
• If children know their doubles facts up to double 10 (double 1, double 2, double 3 etc) they can use these facts to double multiples of 10 and 100.
  Double 2 is 4, double 20 is 40, and double 200 is 400.
• Children can learn to double two-digit numbers by doubling each digit. This works for double 23 (double 2 is 4, double 3 is 6, double 23 is 46) but will not work for double 27 (double 2 is 4, double 7 is 14, double 27 IS NOT
  414). It does not work because the units digit is greater than 4. Children should be made aware that this method is limited in use.
• To double two-digit numbers first partition the number into tens and units. Then double each part of the number before re-combining. To double 27 (20+7) double 20 (=40) then double 7(=14) recombine (40+14) to get 54

ACTIVITY 1: DOUBLING

Activities you can do at home:

Practise doubling the following numbers (use partitioning): 14, 53, 16, 38
Make a doubling chain: 2 double to 4 double to 8 double to 16 double to 32 double to 64….. How many links can you create in your chain before you couldn’t work out the next link? (6 in this chain!)

Good questions to ask:

How can you double this number?
Can you explain what you did first?
How will you partition this number in order to double it?
Which part of it are you going to double first?
If I double a number, how much bigger does it get?

If your child:

Finds it hard to remember common doubles and has to work them out each time
Practise them regularly and start with the easier ones that they know to build confidence. Remind them that by partitioning they can work out answers quite quickly even if they do not know them.