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Partial Progress - Circles (browser only)
Addition and Subtraction
Objectives
To know pairs to 10 and 20 and to write related addition and subtraction facts.
To reason about my maths thinking.
Resources
Abacus Workbook 2 | 20 bead string | Mini whiteboard and pen
Vocabulary
add | plus | subtract | take away | total | bar model | reason
Today's Lesson
Introduction
Remind your student about the way they have been trying to talk about their maths thinking over the past two lessons.
Explain that you will be asking some more ‘Why…?’ or ‘How do you know…?’ questions to help them practise this skill.
Show your student the 📄 Red, blue and yellow cubes picture. This shows a strip of 10 red cubes and below it a strip of 6 blue cubes and 4 yellow cubes (or you could use real interconnecting cubes if you have them).
Say, ‘This picture shows that 6 and 4 cubes is the same amount as 10 cubes. Write 6 + 4 = 10 on the mini whiteboard.’
Point out that we could also have the 4 cubes first and then the 6 cubes, but this would still give 10 cubes
altogether.
Record 4 + 6 = 10.
Ask, ‘If we took away the 4 cubes, how many cubes would be left? How do you know?’
Record 10 – 4 = 6.
Ask, ‘What if we took away the 6 cubes instead?’
Record 10 – 6 = 4.
Point out that we can write four number sentences to go with this one picture! We can call this a Family of Facts!
Explain that it can be time consuming to draw out all the cubes or to keep making sticks of cubes, so we can just draw bars to represent the cubes.
Show the 📄 Bar labelled 10 picture to your student. At the top of this resource is how you would show 6 + 4 using the bar model.
Show the bar model for 5 and 5.
Your student should now write addition and subtractions to go with this picture. Say, ‘This time we only had one addition and one subtraction as it was a double!’
This video demonstrates how to use bar models to show pairs to 10.
Draw a bar model for 16 and 4 making 20, and together write the matching additions and subtractions.
Main Activity
Your student should write the additions and subtractions to go with number pairs shown using the 📄 Fact Family sheet
Encourage your student to use the 20 bead string to help if necessary.
Extra Challenge
Jess the champion sheepdog has to shepherd 20 sheep into two pens.
Say that Jess can’t count, but she knows she has to split the sheep and some have to go into each pen. How might she do it?
What is the most she could have in one pen? How many would be in the other? What additions could we write?
Answer: 20 = 19 + 1 and 20 = 1 + 19, or 19 + 1 = 20 and 1 + 19 = 20.
Jess then has to take another 20 sheep and move some into a ring. What might she do? What subtractions could we write?
Answer (for example): 20 – 3 = 17.
Repeat for some other pairs to 20.
Workbook
To help your student consolidate their learning from today, please ask them to complete the activities on page 11 of Abacus Workbook 2.