1. Mental Addition – Objectives
Use strategies for adding pairs of two-digit numbers to mentally add multiples of 10, and 1000.
You will need:
Mini whiteboards and pens
© Hamilton Trust Simmering Term Week 2 Day 2

2. Mental Addition – Direct Teaching
How would you solve these calculations? =
= 1260
1260 – 10 = 1250
Adding 490 by adding 500 and subtracting 10.
Adding 45 hundreds and 23 hundreds.
Doubling 46 and multiplying by 100. =
46 x 2 = 92
92 x 100 = 9200
Students discuss with a partner. Take responses orally.
Draw out using similar strategies to those used in Week 2 Day 1 session (e.g. adding 490 by adding 500 and subtracting 10). Refer back to slides for modelling of strategies where necessary.
= 6800
Adding 25 thousands and 13 thousands.
25, ,000 = 38,000
© Hamilton Trust Simmering Term Week 2 Day 2

3. Mental Addition – Direct Teaching
25, ,000
= 610 =
= 50
5 + 6 = 11
= 61
= 6100
= 61,000
Students discuss with a partner. Take responses orally.
Draw out using similar strategies to those used in Week 2 Day 1 session (e.g. adding 490 by adding 500 and subtracting 10). Refer back to slides for modelling of strategies where necessary.
© Hamilton Trust Simmering Term Week 2 Day 2

4. Mental Addition – Student Activity
Show me…
Complete each addition:
48, , , ,000
Students discuss with a partner, then show responses on a mini-whiteboard.
Watch out for students who struggle with place value when adding numbers such as 640 and 520; it may help them to see 500 and 600 as making 11 hundred, recording this and then seeing it as one thousand, one hundred.
Challenge:
Can you find two pairs of multiples of 10 with a total of 720?
Can you find two pairs of multiples of 100 with a total of 6800?
© Hamilton Trust Simmering Term Week 2 Day 2

5. Mental Addition – Individual Practice
Choose a number from the grid.
Find which two numbers below the grid have that total.
Can you make 3-in-a-row? 4-in-a-row? 5-in-a-row?
7800
900
63,000
890
6700
80,000
4300
660
74,000
1020
6600
47,000
8700
6000
930
980
8200
810
7300
91,000
45, ,000
62, ,000
45, ,000
29, ,000
Red numbers have a red total, green a green total, and blue a blue total.
Click for answers.
Watch out for students who:
• Have difficulty when the addition means passing through the next multiple of 100/1000, e.g , ; give more practice counting in 10s/100s through multiples of 100/1000
• Struggle with the place value when adding numbers such as 840 and 300; it may help to see 800 and 300 as making 11 hundred, recording this and then seeing it as one thousand, one hundred
• Try to keep all the steps in their head and lose track; encourage them to use jottings, modelling how to use these if necessary.
62, ,000
62, , , ,000
© Hamilton Trust Simmering Term Week 2 Day 2