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Understanding Subtraction, Calculation Strategies

Understanding Subtraction, Calculation Strategies. Lesson 3. Resources: Children’s books. Lob: Using my addition skills to help me to solve subtraction questions. Today we will be learning :. to use place value to subtract pairs of two-digit numbers.

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Understanding Subtraction, Calculation Strategies

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  1. Understanding Subtraction, Calculation Strategies Lesson 3 Resources: Children’s books

  2. Lob: Using my addition skills to help me to solve subtraction questions.

  3. Today we will be learning: • to use place value to subtract pairs of two-digit numbers • to partition a number into tens and units when subtracting.

  4. Mental Activity We are going to play ‘Guess the number’.

  5. A three-digit number has been hidden. You must work out what the number is by asking questions. For example you could ask: “Does the number have fewer than 8 tens?” or “Does it have an even number of units?” You will only be given “Yes” or “No” as answers.

  6. We will try to find the units digit first, then the tens, then the hundreds.

  7. Let’s try another.

  8. Play the same game with your partner on a whiteboard – can you guess their hidden number by asking them questions?

  9. Main Activity Today we are going to look at a way of subtracting by using addition.

  10. 5 3 5 3 2 0 4 0 4 0 2 0 Some subtractions are straight forward….. – We can split these numbers like this… – and and 40 – 20 = 20 5 – 3 = 2 So 45 – 23 = 22

  11. This one is more difficult. 45 – 27 This is more difficult, because 40 – 20 = 20, but 5 – 7 will give a negative number. We can still do the calculation by counting on. Let’s look at a number line to help us.

  12. 18 45 – 27 = +5 +10 +3 30 40 27 45

  13. 40 - 18 22 = 20 2 18 20 40

  14. 34 - 18 16 = 4 10 2 18 20 30 34

  15. 82 - 55 27 = 2 20 5 55 60 80 82

  16. Check 82 - 55 27 = 82 55 + 27 =

  17. Now you try on your whiteboard… 32 - 14 18 = 14 20 30 32

  18. Now you try on your whiteboard… 38 - 19 19 = 19 20 30 38

  19. 72 - 46 26 = 46 50 70 72

  20. 58 - 39 19 = 39 40 50 58

  21. 42 - 13 29 =

  22. 52 - 27 25 =

  23. Well done!!

  24. Today's work: A B C 1. 32-16 1. 65-54 1. 134-42 2. 45-23 2. 69-16 2. 161-33 3. 37-22 3. 62-49 3. 153-25 4. 31-24 4. 87-23 4. 127-48 5. 36-12 5. 86-45 5. 118-45 6. 68-21 6. 76-47 6. 157-34 7. 54-31 7. 94-33 7. 149-37 8. 52-24 8. 63-29 8. 185-58 9. 62-43 9. 75-47 9. 184-67 10. 52-45 10. 72-59 10. 177-66 11. 352-246

  25. Plenary Marking and discussing answers A B C 1. 32-16=16 1. 65-54=9 1. 134-42=92 2. 45-23= 2. 69-16= 2. 161-33= 3. 37-22= 3. 62-49= 3. 153-25= 4. 31-24= 4. 87-23= 4. 127-48= 5. 36-12= 5. 86-45= 5. 118-45= 6. 68-21= 6. 76-47= 6. 157-34= 7. 54-31= 7. 94-33= 7. 149-37= 8. 52-24= 8. 63-29= 8. 185-58= 9. 62-43= 9. 75-47= 9. 184-67= 10. 52-45= 10. 72-59= 10. 177-66= 11. 352-246=

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