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Addition and Subtraction
Objectives
To know addition and subtraction facts for 10 and 20.
To use these facts in adding three numbers
Resources
Abacus Workbook 1 | 📄 20 grid | Sticky notes | Mini whiteboard and pen | 📄 1-20 Number cards
Vocabulary
number pairs | number bonds | add | addition fact | subtract | subtraction fact
Today's Lesson
Introduction
Show your student the 📄 20 grid resource.
Ask, ‘How many parts are there on each line? And altogether?’
Hide 3 parts on the top row behind a sticky note. Point out that we can see 7, so they know 3 must be hidden because 7 + 3 = 10.
Record 7 + 3 = 10.
Write 17 + _ = 20. Ask, ‘How many parts would now be hidden? So what number is missing?’
Repeat, hiding other numbers of parts from one row behind sticky notes and encouraging your student to use their pairs to 10 to work out the missing number.
Next, write the addition 17 + 5 + 3 on the whiteboard.
Ask, ‘How might we solve this?’ Hopefully they will spot the pair to 20 (17 + 3 = 20) to start with.
Agree that 17 + 3 is 20, so we know that the whole addition must be 20 + 5 or 25. Explain that, if we have three numbers to add and can spot a bond to 10 or 20, it helps to find the total!
Write these four additions on the whiteboard:
8 + 13 + 2
9 + 5 + 11
3 + 15 + 7
14 + 7 + 6
Ask your student to choose one of the additions and to look for a pair of numbers that makes either 10 or 20.
Give them a minute to solve the addition. Then take each one in turn and solve it – first by spotting the pair to 10 or 20, then adding the third number.
This video demonstrates the above strategy of using number bonds to add together sets of 3 numbers.
Main Activity
Spread out a set of 📄 1-20 Number cards face up on the table and play this game with your student.
Each take one card, but your two cards together must total either 10 or 20.
Then one of you should take a third card and you should then discuss together what the total of all three cards is.
Ask your student to record the addition on paper.
Play again, replacing the cards face up.
Repeat this at least seven times, so that your student has eight additions in total recorded.
Challenge your student to ensure that each of their additions uses a different bond to 10 or 20.
Workbook
To help your student consolidate their learning from today, please ask them to complete the activities on page 56 of Abacus Workbook 1.