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Using number lines in Addition and Subtraction By Amani El-Alawneh Adding numbers using the number line. 25 47 So how do we do this using the number line? We use the strategy called: Counting Up You need to think about: What number shall I start with on my number line? What number do we want to count up by? Are there any number bonds that can help me? 25 + 47 = Use the counting up method!! +20 +3 47 67 +2 70 72 So we start at the biggest number…47 And count up 25 places What number do we end on??? So…. 25 + 47 = 72 ? + 34 = 57 Use the Counting Strategy Up Remember -You need to think about: What number shall I start with on my number line? What number do we want to count up by? Are there any number bonds that can help me? + 34 = 57 +10 +10 34 +3 44 54 34 So what is 10 + 10 + 3 = 23 So….. 23 + 34 = 57 57 57 Can I use the counting up strategy for Subtraction too? YES Have a look at this question! 43 – 27 = 16 What number shall I start from on my number line? What number do I want to get to? What number shall count on by? Can any number bond make counting on easier for me? +10 27 10 + 3 + 3 = 16 +3 37 +3 40 43 32 - = 18 What number shall I start from on my number line? What number do I want to get to? What number shall count on by? Can any number bond make counting on easier for me? +10 +2 +2 18 20 30 2 + 10 + 2 = 14 So…. 32 - 14 = 18 32 Have a go at these questions now using number lines and the counting on strategy: 1. 2. 3. 4. 5. 45 – 25 = 54 – 26 = – 19 =36 28 – = 14 43 – 37 = 6. 55 + 18 = 7. 29 + 40 = 8. 33 + 9. = 51 + 14 = 35 10. 22 + 15 = Extra for Experts: 1. 154 – 147 6. 123 + 19 2. 172 – 133 7. 199 + 98 3. 198 – 188 8. 147 + 76 4. 134 – 119 9. 201 + 97 5. 176 - 134 10. 185 + 89 Work out the following calculations mentally: • • • • 43 – 37 102 – 98 154 – 147 3005 – 2997 How can we show this using the number line: 43 – 37 +3 +3 37 3+3=6 So, 40 43 – 37 = 6 43 154 – 147 +4 +3 3+4=7 So, 147 150 154 154 – 147 = 7 Have a look at these Calculations • 144 – 138 • 89 – 34 What is it about the numbers that made you decide to use mental method or a number line? • 134 – 123 • 125 - 76 Do you always need to use a number line when the numbers are a long way apart?? - 285 = 39 + + 285 300