1. Addition and Subtraction Mental addition of 2-digit numbers
Objectives
Day 1
Add pairs of 2-digit numbers using different strategies.
Day 2
Before teaching, be aware that:
On Day 1 children will need mini-whiteboards and pens. Use a large 1 to 100 number grid, plastic/card spider and fly for modelling additions.
On Day 2 children will need mini-whiteboards and pens.
Year 3

2. Addition and Subtraction Mental addition of 2-digit numbers
Starters
Day 1
Add multiples of 10 (pre-requisite skills)
Day 2
Add 3 or 4 numbers (pre-requisite skills)
Choose starters that suit your class by dragging and dropping the relevant slide or slides below to the start of the teaching for each day.
Year 3

3. Addition and Subtraction Mental addition of 2-digit numbers
Starter
Add multiples of 10
Pre-requisite skills – to use this starter, drag this slide to the start of Day 1
Review Spider counting in 10s on a large grid. Remember that Spider lives on the 100-square and can only go up and down it, counting up and down in 10s as she goes. Say a 2-digit number less than 50 and throw a multiples-of-10 dice (10–60). Who can be first to add the 2 together and show the answer on their whiteboards? Discuss and repeat.
Year 3

4. Addition and Subtraction
Mental addition of 2-digit numbers
Starter
Add 3 or 4 numbers (pre-requisite skills)
Pre-requisite skills – to use this starter, drag this slide to the start of Day 2
Model playing Flippy Floppy Fingers at the front, in groups of 3. Children shake their fingers saying flippy floppy fingers. They reveal any number of fingers and then have to add the total fingers of their group before the others in the group do. Focus on spotting pairs that make 10 and doubles. Children working at Greater Depth to do this in groups of 4.
Year 3

5. Addition and Subtraction Mental addition of 2-digit numbers
Objectives
Day 1
Add pairs of 2-digit numbers using different strategies.
Year 3

6. Day 1: Add pairs of 2-digit numbers using different strategies.
Work out then discuss in pairs how you solved it.
What strategies did you use?
One way is to start with the larger number, count on 20 then 5….
Another way is to partition the two numbers then add the 10s and 1s and recombine.
… so = 55
and = 58.
… so = 50
and = 8.
Then = 58
Year 3

7. Day 1: Add pairs of 2-digit numbers using different strategies.
Remember Spider counts on or back in 10s…
For adding a near multiple we can use Spider and Fly on a 100 square...
Let’s try
Spider starts at 47.
He jumps down
2 squares (two tens) to 67.
…and Fly counts on or back in 1s.
21 is 1 more than 20 so count on 1 with fly.
So, = 68
Year 3

8. This time fly goes back 1 since 19 is What will fly do this time?
Day 1: Add pairs of 2-digit numbers using different strategies.
Let’s try
He jumps down
2 squares to 85.
Spider starts at 65.
This time fly goes back 1 since 19 is
1 less than 20.
What will fly do this time?
So = 84.
Year 3

9. Day 1: Add pairs of 2-digit numbers using different strategies.
Work with a partner, finding other pairs of
2-digit numbers to add.
Can you find a pair for each strategy?
Let’s check some of those on the 100 square or flipchart.
Let’s make a list on our class display of some of our strategies, e.g. partition
look for number bonds
look for near multiples
use Spider and Fly
put the larger number first.
Today would be a great day to use a problem-solving investigation – Dicey addition – as the group activity, which you can find in this unit’s IN-DEPTH INVESTIGATION box on Hamilton’s website.
Alternatively, children can now go on to do differentiated GROUP ACTIVITIES. You can find Hamilton’s group activities in this unit’s TEACHING AND GROUP ACTIVITIES download on our website.
WT: Use spinners (Sheet 1) to generate 2-digit numbers to add. Children discuss which strategy to use each time.
ARE/GD: Use spinners (Sheet 2) to generate 2-digit numbers to add. Children discuss which strategy to use each time.
Year 3

10. Year 3 The Practice Sheet on this slide is suitable for most children.
Differentiated PRACTICE WORKSHEETS are available on Hamilton’s website in this unit’s PROCEDURAL FLUENCY box.
WT: Adding pairs of 2-digit numbers Sheet 1.
ARE: Adding pairs of 2-digit numbers Sheet 2.
GD: Adding pairs of 2-digit numbers Sheet 2, then find total of pairs greater than £1.
Year 3

11. Addition and Subtraction Mental addition of 2-digit numbers
Objectives
Day 2
Add pairs of 2-digit numbers using different strategies.
Year 3

12. Look for near multiples. Put the larger number first.
Day 2: Add pairs of 2-digit numbers using different strategies.
Who can remember some of our strategies for adding two 2-digit numbers?
Partition into 10s and 1s.
Look for number bonds.
Look for near multiples.
Use Spider and Fly.
Today we will use all these to find the most efficient ways to add three 2-digit numbers.
Put the larger number first.
Year 3

13. How could we find the total length of these 3 ribbons?
Day 2: Add pairs of 2-digit numbers using different strategies.
18cm
25cm
43cm
How could we find the total length of these 3 ribbons?
Let’s try partitioning into 10s and 1s and putting the larger numbers first.
= ?
= ?
= ?
Year 3

14. What about these three ribbons?
Day 2: Add pairs of 2-digit numbers using different strategies.
23cm
57cm
48cm
What about these three ribbons?
Let’s try partitioning into 10s and 1s. Did you spot the pair of 1s that make 10?
= ?
= ?
= ?
Year 3

15. Day 2: Add pairs of 2-digit numbers using different strategies.
65 , 35 and 21.
5 + 5 = 10 to help us add the 1s.
Are there three of these numbers that would be straightforward to add?
Which group of three could be trickiest?
= ?
48, 65 and 27 could be trickier…
Let’s try partitioning.
Children can now go on to do differentiated GROUP ACTIVITIES. You can find Hamilton’s group activities in this unit’s TEACHING AND GROUP ACTIVITIES download on our website.
WT: Choose two 2-digit numbers to add, ring answer on a grid. Try to get 3 in a line.
ARE/GD: Choose three 2-digit numbers to add, ring answer on a grid. Try to get 3 in a line.GD:
= ?
= ?
Year 3

16. Challenge
The Practice Sheet on this slide is suitable for most children.
Differentiated PRACTICE WORKSHEETS are available on Hamilton’s website in this unit’s PROCEDURAL FLUENCY box.
WT: Complete as many of the first 10 as they can.
ARE: Questions 1 to 12.
GD: Questions 5 to 16.
Year 3

17. Addition and Subtraction Mental addition of 2-digit numbers
Well Done! You’ve completed this unit.
Objectives
Day 1
Add pairs of 2-digit numbers using different strategies.
Day 2
You can now use the Mastery: Reasoning and Problem-Solving questions to assess children’s success across this unit. Go to the next slide.
Year 3

18. Problem solving and reasoning questions
Use a different strategy for each of these additions:
(a)
(b)
(c)
(d)
Explain why you chose a particular strategy for (a) and (c)
Complete the bar model diagrams: ? 36 37 ? 57 39 ? 48 24
Year 3