1. Mental Addition – Objectives
Work out, very quickly, pairs of one-place decimal numbers with a total of 1, then 10;
Add pairs of one-place decimal numbers.
You will need:
stopwatch or clock/watch with second hand
© Hamilton Trust Keeping Up Term Week 7 Day 1

2. Mental Addition – Direct Teaching
Quickly write down the pairs of numbers 0-10 that add to 10. Can you write them all in 1 minute?
Now use the cards below to find pairs to make 1
Can you write them all in 1 minute?
0.9
0.5
0.4
0.1
0.3
Challenge pupils to write the bonds to 10 in one minute.
Point out that this knowledge to helps us write the pairs of one-place decimals to make 1.
0.5 has to be added to itself – which is why it occurs twice.
0.2
0.7
0.6
0.5 1
0.8
Why is the same number on two cards?
© Hamilton Trust Keeping Up Term Week 7 Day 1

3. Mental Addition – Direct Teaching
Which decimal numbers together make 10?
2.6 10
3.0
0.4 7
Use a number line jotting to work out what goes with 4.3, 6.1, 5.8 and 8.9 to make 10.
© Hamilton Trust Keeping Up Term Week 7 Day 1

4. Mental Addition – Student Activity
Work in pairs. Repeat this activity five times.
Write five one-place decimal numbers secretly on your page.
Take turns to say a one-place decimal number less than 1 to your partner. For example say 0.6.
Does this go with any of their numbers to make a whole number? For example one of their numbers is 8.4, so yes!
They score the amount they need to add to their number to make 10. For example = 10. Score 1.6.
Swap roles, with your partner saying a similar number to you.
The winner is the player with the highest score after five goes.
Encourage pupils to use a number line jotting to work out the bond to 10.
So 8.4 add 0.6, then add 1. Once they get used to counting up in this way, they will find it quick and easy and gain in fluency and confidence.
© Hamilton Trust Keeping Up Term Week 7 Day 1

5. Mental Addition – Direct Teaching
We use pairs to 1 to add two decimal numbers.
4.6
7.3
5.0
0.4
2.0
0.3
Remind pupils that we can use pairs to 1 to add the first part of a decimal number – the subsequent additions are easy.
Demonstrate with the number line. Encourage pupils to use the number line jotting. It makes it easy!
5.3
Use a number line jotting to work out:
and
© Hamilton Trust Keeping Up Term Week 7 Day 1

6. Mental Addition – Student Activity
Use pairs to 1 and a number line jotting to solve these calculations:
© Hamilton Trust Keeping Up Term Week 7 Day 1

7. Mental Addition – Individual Practice
Fill in the missing numbers.
☐ = ☐ = 10
= ☐ = ☐
= ☐ = ☐
= ☐ ☐ = 10
☐ = ☐ = 1
= ☐ = ☐
= ☐ ☐ = 10
Q1 to 6 should be done by all pupils. After that more able pupils do odd numbers, less able do even numbers.
© Hamilton Trust Keeping Up Term Week 7 Day 1