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‘Counting up to’ strategy

‘Counting up to’ strategy. 20/02/14. Adding and subtracting. To add or subtract large numbers, your first strategy is to try and work out the answer in your head. This is a quicker and easier (once you get the hang of it) way to work out the answer.

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‘Counting up to’ strategy

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  1. ‘Counting up to’ strategy 20/02/14

  2. Adding and subtracting To add or subtract large numbers, your first strategy is to try and work out the answer in your head. This is a quicker and easier (once you get the hang of it) way to work out the answer. The idea is to count up to the higher number.

  3. Mental maths So instead of using a calculator we are going to use our heads to estimate the sum or difference between 2 numbers. When we are ‘counting on’ we need to round up to the nearest 5, 10, 50, 100, 500 or 1000 (or more if you want a challenge!). It just depends on the size of the numbers you are working with.

  4. examples Let’s try and add the number 342 to the next 1000 342 1000 You would add 8 to make 350. You add 50 more to make 400. You would add 600 more to make 1000. So altogether that’s 658 more to make 1000.

  5. Your go! Now we are going to try the number 734. Let’s add to the next 1000. 734 1000 What will we add to make 740? What will we then add to make 800? Now how many will we add to make 1000? So how much altogether to get to 1000? 6 60 200 6 + 60 + 200 = ?

  6. Number lines We can use a number line to help our thinking and to show our working out. Let’s use the number 567 and add to the next 1000. 567 1000 3 30 400 567 570 600 1000

  7. Task 1 Use a ‘counting up to’ strategy to work out the difference for these number sentences. Demonstrate at least one on a number line. Remember to show your working out! 1. 256 + = 500 2. 481 + = 1000 3. 805 + = 1000 More on the next page!

  8. Task 2 continued 4. 213 + = 500 5. 666 + = 1000 6. 1132 + = 1500 Well done! Read onto the next slide if you are up for a challenge! Otherwise grab a maths task card and away you go!

  9. Real life examples Sometimes we need to use the count up to strategy to find the difference between two numbers. Maybe we need to find the difference between the price of 2 different bikes. Can you think of another example? In this case we wouldn’t necessarily be counting up to a neat number like 1000. Lets look at the next example together…

  10. Distance What is the difference in length between these 2 rivers? Nile River 6693 km long Amazon River 6436 km long You will need to start at 6436 and count up to 6693

  11. Using a number line If we use a number line we can count up much easier. Amazon River 6436 km, Nile River 6693 km 4 60 100 93 6436 6440 6500 6600 6693 So if we add them all together what is the difference? 4 + 60 + 100 + 93 =

  12. Task 2 What is the difference in length between these 2 Chinese rivers? Chang Jiang River 6370 km Huang He River 5464 km

  13. Task complete! Well done! Fantastic work! Now grab a maths task card and away you go!

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