Addition and Subtraction

Objectives

To double and halve by partitioning.

Resources

Interactive Place Value (Mathsframe) | 📄 Halving and Doubling | Halve and Doubles game (TopMarks) | Archery Doubles (ICT Games)

Vocabulary

double | halve | partition | inverse

Today's Lesson

What to Get Ready

Familiarise yourself with the Interactive Place Value website.

EXPLORE - Interactive Place Value (Mathsframe)

The arrow cards show the value of the digits in 2-digit numbers, for example, that 67 is made up of a 60 and a 7.

Once familiar, show your student how the resource works, asking them to create some 2-digit numbers, so that they get used to how the controls work.

Introduction

Remind your student that doubling is when we add a number to itself: we have two lots of that number.

Show on the Interactive Place Value website how to create 14 by selecting a 10 and a 4.

EXPLORE - Interactive Place Value (Mathsframe)

Create this again so that there are two lots of 14.

Ask: ‘What is double 10? What is double 4?’

Record:

14 + 14

= 10 + 10 + 4 + 4

= 20 + 8

= 28

Now ask your student to do the same with the number 23 on the interactive resource.

Record as above:

23 + 23

= 20 + 20 + 3 + 3

= 40 + 6

= 46

Repeat for double 34, 42 and then 46. For the latter, record the partitioning as above and note, ‘This time the ones cards came to more than 10. How will we find 80 + 12?’ Discuss how we can further partition 12 to 10 and 2 to help with the addition if needed.

Explain that we can use this strategy to halve too.

Show 46 on the interactive resource, partitioned as 40 + 6.

Model halving the 40 and 6 to give 20 + 3, then recombining to make 23.

Explain that we can check our answer by doubling the number to see if it gives the number we started with. Doubling and halving are opposites – in Maths we say that they are the inverse of one another.

This video demonstrates using the arrow cards from Maths Frame as a strategy to double and halve.

Repeat to find half of 24, 66 and 34.