1. Mental Addition – Objectives
Work out, very quickly, pairs with a total of 100;
Add pairs of 2-digit numbers.
You will need:
1-9 digit cards (one set per two students)
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2. Mental Addition – Direct Teaching
=33
Handy Hint
Look for the bond to 10 for the ones digit and the bond to 9 for the tens digit… +3
+30
How many more to make 100?
© Hamilton Trust Keeping Up Term Week 2 Day 1

3. Mental Addition – Student Activity
With a partner, shuffle a pack of 1 to 9 digit cards.
Take it in turns to take the top 2 and use them
to make a 2-digit number.
Work out what is needed to make 100. 2 4
Watch out for students who think that 47 needs to be added to 63 to make 100 for example, because they look for tens which add to 100, not 90.
Also watch out for students do not have instant recall of number facts for addition of single-digit numbers. 3 5 7 6 8 9 1
© Hamilton Trust Keeping Up Term Week 2 Day 1

4. Mental Addition – Direct Teaching
What strategies could you use to solve these calculations?
Ask students to discuss in pairs how they might solve the additions shown.
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5. Mental Addition – Direct Teaching Partitioning and Recombining
Add the 10s
110
Add the 1s
7 + 8 15
Partition
Take students’ suggestions, then model this strategy.
125
Recombine =
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6. 74 + 19 Mental Addition – Direct Teaching 93 74
Add the nearest multiple of 10 and adjust 74 93 94
Simple!
+20 -1
>
<
Take students’ suggestions, then model this strategy.
© Hamilton Trust Keeping Up Term Week 2 Day 1

7. 2 4 3 7 9 6 5 8 Mental Addition – Individual Practice or
Create pairs of 2-digit numbers using: 2 4 3 7 or 9 6 5 8
The blue box is slightly trickier, as it will result in more pairs where the ones digit totals more than 10.
Take feedback on the biggest and smallest possible answers.
Watch out for students who:
• do not have instant recall of number facts for addition of single-digit numbers;
• have difficulty when the addition means passing through the next multiple of 100, e.g ; give more practice counting in 10s through multiples of 100.
Add the pairs together.
How many different totals can you make?
© Hamilton Trust Keeping Up Term Week 2 Day 1