1. Mental Addition: Objectives
Work out, very quickly, pairs with a total of 100
Add pairs of 2-digit numbers
You will need: pdf of grid and one for each pair of pupils (see resources), 1-9 digit cards
© Hamilton Trust Keeping Up Term Week 2 Day 1

2. Mental Addition: Teacher Led
Display the 1 to 100 grid. Ring a number, e.g. 67 and ask how many more are needed to make 100. Pupils write the answer on their whiteboards. Point out the 3 to reach the end of the row, 70, and then 30 (3 tens) to reach 100.
Ring other two-digit numbers asking pupils to find the complement to 100 each time.
Give pupils the hint: Look for bond to 10 for the units, and bond to 9 for the tens (as the units make one of the tens).
© Hamilton Trust Keeping Up Term Week 2 Day 1

3. Mental Addition: Student Activity
Work in pairs.
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 and ring this number on a grid.
For example, if you take 6 and 2 to make 62, ring 38, or choose use 6 and 2 to make 26, and so ring 74.
Carry on playing like this until one person rings three numbers in a line to win.
You will need: pdf of grid and one for each pair of pupils (see resources), 1-9 digit cards
Watch out for pupils 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 pupils do not have instant recall of number facts for addition of single-digit numbers.
© Hamilton Trust Keeping Up Term Week 2 Day 1

4. Mental Addition: Teacher Led
What strategies could you use to solve these calculations?
Ask pupils to discuss in pairs how they would solve the additions shown.
Draw out strategies such as partitioning and recombining (e.g = = = 125) OR adding the nearest multiple of 10 and adjusting (e.g = – 1 = 94 – 1 = 93).
© Hamilton Trust Keeping Up Term Week 2 Day 1

5. Mental Addition: Student Activity
Create pairs of 2-digit numbers using
Add the pairs together.
How many different totals can you make?
Take feedback on the biggest and smallest possible answers.
Watch out for pupils 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;
© Hamilton Trust Keeping Up Term Week 2 Day 1