Addition and Subtraction Mental addition and subtraction 1

Addition and Subtraction Mental addition and subtraction (1) Objectives Day 1 Y 2: Identify number facts and strategies for solving addition questions. Y 3: Add pairs of 2 -digit numbers using different strategies. Day 2 Y 2: Identify number facts and strategies for solving subtraction questions. Y 3: Add three 2 -digit numbers using different strategies. © hamilton-trust. org. uk 1 Year 2/3

Addition and Subtraction Mental addition and subtraction (1) Short Mental Workouts Day 1 Pairs to 20 Day 2 Add 3 or 4 numbers © hamilton-trust. org. uk 2 Year 2/3

Addition and Subtraction Mental addition and subtraction (1) Short Mental Workout Pairs to 20 © hamilton-trust. org. uk 3 Year 2/3

Addition and Subtraction Mental addition and subtraction (1) Short Mental Workout Add 3 or 4 numbers © hamilton-trust. org. uk 5 Year 2/3

Addition and Subtraction Mental addition and subtraction (1) Objectives Day 1 Y 2: Identify number facts and strategies for solving addition questions. Y 3: Add pairs of 2 -digit numbers using different strategies. © hamilton-trust. org. uk 6 Year 2/3

Day 1: Y 2: Identify number facts and strategies for solving addition questions. Y 3: Add pairs of 2 -digit numbers using different strategies. 7+7 10 + 6 9+3 6+4 15 + 5 We could solve all of these answers by counting on, but Let’s see what we’ve found some might be easier to solve out… using number facts we have learned. 7+7 We can use doubles! 4+7 18 + 5 20 + 7 Talk to your partner. Which of these can we +4 solve using 6 number we know? Wefacts can use number bonds to 10. 15 + 5 We can use pairs that make 20. © hamilton-trust. org. uk 7 Year 2/3

Day 1: Y 2: Identify number facts and strategies for solving addition questions. Y 3: Add pairs of 2 -digit numbers using different strategies. 7+7 10 + 6 9+3 6+4 15 + 5 We can also use place value for some… remember how we use place value cards… 10 + 6 = 16, any others like that? © hamilton-trust. org. uk 8 4+7 18 + 5 1 0 6 2 0 7 20 + 7 Year 2/3

Day 1: Y 2: Identify number facts and strategies for solving addition questions. Y 3: Add pairs of 2 -digit numbers using different strategies. 7+7 9+3 10 + 6 7+7 6+4 10 + 6 6+4 15 + 5 20 + 7 4+7 9+3 15 + 5 18 + 5 20 + 7 4+7 18 + 5 Solve by using place value/number facts Solve by counting on There is often more than one We can sort the questions But we should try to spot the way of solving a problem in into 2 groups… most efficient and quickest maths. That’s helpful for way to solve a problem. checking! © hamilton-trust. org. uk 9 Year 2/3

Challenge © hamilton-trust. org. uk 10 Year 2/3

Day 1: Y 3: Add pairs of 2 -digit numbers using different strategies. Calculate 23 + 35 then discuss in pairs how you solved it. What strategies did you use? Another way is to partition the two numbers, then add the 10 s and 1 s and recombine. One way is to start with the larger number, count on 20 then 3…. … so 35 + 20 = 55 and 55 + 3 = 58 © hamilton-trust. org. uk … so 20 + 30 = 50 and 3 + 5 = 8. Then 50 + 8 = 58 11 Year 2/3

Day 1: Y 3: Add pairs of 2 -digit numbers using different strategies. For adding a near Let’swe trycan use multiple 47 +Fly 21 on a 100 Spider and square. . . Remember Spider counts Spider starts at 47. on or back in 10 s… He jumps down 2 squares (two tens) to 67. …and Fly counts on 21 is 1 more than 20 or back in 1 s. so count on 1 with fly. So, 47 + 21 = 68 © hamilton-trust. org. uk 12 Year 2/3

Day 1: Y 3: Add pairs of 2 -digit numbers using different strategies. Let’s try 65 + 19 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 65 + 19 = 84. © hamilton-trust. org. uk 13 Year 2/3

Day 1: Y 3: Add pairs of 2 -digit numbers using different strategies. Let’s check some of those on the 100 square or flipchart. With a partner, find other pairs of 2 -digit numbers to add. Can you find a pair for each strategy? 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. © hamilton-trust. org. uk 14 Year 2/3

Addition and Subtraction Mental addition and subtraction (1) Objectives Day 2 Y 2: Identify number facts and strategies for solving subtraction questions. Y 3: Add three 2 -digit numbers using different strategies. © hamilton-trust. org. uk 16 Year 2/3

Day 2: Y 2: Identify number facts and strategies for solving subtraction questions. Y 3: Add three 2 -digit numbers using different strategies. 26 - 6 30 - 7 13 - 4 20 - 8 Just as some of the additions we looked at in the last lesson We can be useanswered number facts. could using 7 + 2 = facts 9 so 9 to- 2 help, = 7. the learned same is true of these subtractions. 9 -2 14 - 4 23 - 7 Talk to your partner. Which of these can webonds We can use number solve usingtonumber 20. facts we know? We know 20 - 7 = 13 so 30 – 17 must be 10 more! © hamilton-trust. org. uk 17 Year 2/3

Day 2: Y 2: Identify number facts and strategies for solving subtraction questions. Y 3: Add three 2 -digit numbers using different strategies. 26 - 6 30 - 7 13 - 4 20 - 8 9 -2 We can also use place value for some… remember how we use place value cards… 1 04 14 - 4 = 10. Are there any others like that? 2 06 © hamilton-trust. org. uk 18 14 - 4 23 - 7 Year 2/3

Day 2: Y 2: Identify number facts and strategies for solving subtraction questions. Y 3: Add three 2 -digit numbers using different strategies. 26 - 6 30 - 7 13 - 4 9 -2 14 - 4 20 - 8 30 - 7 9 -2 14 - 4 23 - 7 Solve by using place value/number facts 23 - 7 13 - 4 Solve by counting back There is often more than one We can sort the questions But just like with addition we way of solving a problem in into 2 groups…should try to spot the most maths. That’s helpful for efficient and quickest way to checking! solve a problem. © hamilton-trust. org. uk 19 Year 2/3

Challenge © hamilton-trust. org. uk 20 Year 2/3

Day 2: Y 3: Add three 2 -digit numbers using different strategies. Who can remember some of our strategies for adding two 2 -digit numbers? Look for number bonds. Partition into 10 s and 1 s. Look for near multiples. Use Spider and Fly. Put the larger number first. © hamilton-trust. org. uk Today we will use all these to find the most efficient ways to add three 2 -digit numbers. 21 Year 2/3

Day 2: Y 3: Add three 2 -digit numbers using different strategies. 18 cm 43 cm 25 cm How could we find the total length of these 3 ribbons? 40 + 20 + 10 = ? Let’s try partitioning into 10 s and 1 s and putting the larger numbers first. 8+5+3=? 70 + 16 = ? © hamilton-trust. org. uk 22 Year 2/3

Day 2: Y 3: Add three 2 -digit numbers using different strategies. 23 cm 57 cm 48 cm What about these three ribbons? Let’s try partitioning into 10 s and 1 s… 50 + 40 + 20 = ? And did you spot the pair of 1 s that make 10? 8+7+3=? 110 + 18 = ? © hamilton-trust. org. uk 23 Year 2/3

Day 2: Y 3: Add three 2 -digit numbers using different strategies. 65 27 35 31 48 Are there three of these numbers that would be straightforward to add? Which group of three could be trickiest? 65 , 35 and 21. 5 + 5 = 10 to help us add the 1 s. 60 + 40 + 20 = ? 48, 65 and 27 could be trickier… Let’s try partitioning. 8+7+5=? 120 + 20 = ? © hamilton-trust. org. uk 24 Year 2/3

Investigation Use the in-depth problem-solving investigation ‘Dicey addition’ from NRICH as today’s Y 3 group activity, or use the Day 2 Group Activities shown on the Planning download. © hamilton-trust. org. uk 25 Year 2/3

Challenge © hamilton-trust. org. uk 26 Year 2/3

Addition and Subtraction Mental addition and subtraction (1) Well Done! You’ve completed this unit. Objectives Day 1 Y 2: Identify number facts and strategies for solving addition questions. Y 3: Add pairs of 2 -digit numbers using different strategies. Day 2 Y 2: Identify number facts and strategies for solving subtraction questions. Y 3: Add three 2 -digit numbers using different strategies. © hamilton-trust. org. uk 27 Year 2/3

Problem solving and reasoning: Questions Year 2 Solve each of these additions using a different strategy. Say how you did each one. 30 + 9 = 17 + 5 = 4+7+6= Solve each of these subtractions using a different strategy. Say how you did each one. 25 – 5 = 14 – 6 = 58 – 4 = © hamilton-trust. org. uk 28 Year 2/3

Problem solving and reasoning: Questions Year 3 Use a different strategy for each of these additions: (a) 45 + 29 (b) 45 + 34 (c) 65 + 35 (d) 78 + 28 Explain why you chose a particular strategy for (a) and (c) Complete the bar model diagrams: Solve: 23 + 40 + 36 35 + 27 + 35 28 + 17 + 46 © hamilton-trust. org. uk 29 Year 2/3

Problem solving and reasoning: Answers Year 2 Solve each of these additions using a different strategy. Say how you did each one. 30 + 9 = 39 – place value addition. 17 + 5 = 22 – bridging 20, i. e. solving as 17 + 3 + 2. 4 + 7 + 6 = 17 - spotting the number bond to 10 (4 + 6). These, and for the following question, are examples only, children may use other strategies. Where they have simply given an answer, challenge them to explain; some may be able to verbalise their strategies without being able to give a written explanation. Solve each of these subtractions using a different strategy. Say how you did each one. 25 – 5 = 20 – place value subtraction. 14 – 6 = bridging 10, i. e. solving as 14 – 2 58 – 4 = using the number fact for 8 – 4. © hamilton-trust. org. uk 30 Year 2/3

Problem solving and reasoning: Answers Year 3 Use a different strategy for each of these additions: (a) 45 + 29 = 74 Add 30 and subtract 1 (add and adjust). (b) 45 + 34 = 79 Add 30 then 4 (or partition and add). (c) 65 + 35 = 100 Complements to 10 or 100. (d) 78 + 28 = 106 Partition, add and recombine. Explain why you chose a particular strategy for (a) and (c) Children may use other strategies but are they the most efficient? The key thing is to look at the numbers and see what they suggest might be the most efficient. Complete the bar model diagrams: Solve: 23 + 40 + 36 = 99 Do children spot that counting on is probably the most efficient strategy for this calculation, since the 1 s total is <10? 25 + 27 + 35 = 87 Did children spot the pair that added to a multiple of 10 (25 + 35= 60)? 28 + 17 + 46 = 91 Partitioning and recombining was probably the most sensible strategy here: 20 + 10 + 40 = 70; 8 + 7 + 6 = 21. 70 + 21 = 91 © hamilton-trust. org. uk 31 Year 2/3