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Addition and Subtraction

To work out what number symbols stand for.

To use addition facts.

Abacus Workbook 3 | Mini whiteboard and pen

number symbol

Watch this video together. Have your whiteboard and pen ready.

Write ■ + ▲ = 15 on the mini whiteboard.

Say that there are two mystery numbers in this sentence. Ask, ‘What could they be?’

Say, ‘If the square is 8, what is the triangle worth? How do we know?’

Point out that if the square is 8, then the triangle must be the number that goes with 8 to make 15, which is 7.

Ask, ‘What if the square was worth 1?’

Then write 10 + ■ + ▲ = 16 on the mini whiteboard. Ask ‘What could the mystery numbers be now?’

Ask, ‘How much has been added on to 10 to make 16? So what possible pairs of numbers can make 6?’

Write down your student's suggestions.

Repeat with 8 + ■ + ▲ = 16.

Then write 20 - ■ - ▲ = 15.

Talk to your student about how this is a subtraction number sentence. Ask, ‘How much has been taken away altogether? How do you know?’

Then ask your student to suggest how much the triangle and square could be worth.

Repeat with 10 - ■ - ▲ = 5.

Ask your student to make up two of their own Missing Number problems for you or someone else to solve.

Show your student this addition grid:

Ask, ‘How do you think the grid works?’

Discuss how 8 and 3 makes 11, and 7 and 4 make 12.

Ask your student to make some suggestions about what the mystery number might be, and try out their ideas.

Repeat for the second square below.

To help your student to recap upon previous learning from this course, please ask them to complete the activities on page 6 of Abacus Workbook 3.