Mental Addition – Objectives Use strategies for adding pairs of two-digit numbers to mentally add multiples of 10, 100 and 1000. You will need: Mini whiteboards and pens © Hamilton Trust Simmering Term 1 Week 2 Day 2

Mental Addition – Direct Teaching How would you solve these calculations? 760 + 490 = 760 + 500 = 1260 1260 – 10 = 1250 Adding 490 by adding 500 and subtracting 10. Adding 45 hundreds and 23 hundreds. Doubling 46 and multiplying by 100. 4600 + 4600 = 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. 4500 + 2300 = 6800 Adding 25 thousands and 13 thousands. 25,000 + 13,000 = 38,000 © Hamilton Trust Simmering Term 1 Week 2 Day 2

Mental Addition – Direct Teaching 250 + 360 2500 + 3600 25,000 + 36,000 = 610 25 + 36 = 20 + 30 = 50 5 + 6 = 11 50 + 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 1 Week 2 Day 2

Mental Addition – Student Activity Show me… Complete each addition: 420 + 350 560 + 490 5600 + 3700 8600 + 8600 48,000 + 24,000 57,000 + 25,000 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 1 Week 2 Day 2

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 4200 + 3600 270 + 630 45,000 + 18,000 540 + 350 3600 + 3100 62,000 + 18,000 1900 + 2400 270 + 390 45,000 + 29,000 630 + 390 4200 + 2400 29,000 + 18,000 6300 + 2400 3600 + 2400 540 + 390 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. 840 + 300, 785 + 50; 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. 630 + 350 6300 + 1900 540 + 270 4200 + 3100 62,000 + 29,000 270 540 350 390 630 1900 6300 4200 3600 2400 3100 62,000 45,000 29,000 18,000 © Hamilton Trust Simmering Term 1 Week 2 Day 2