Problems like-73-19-
- 1. Problems like 73 – 19 = ….. I am learning to solve division problems like 73 - 19 = … by first subtracting a tidy number and then adding on a small number to get the answer. Numbers like 10, 20, 30, 40 etc.
- 2. SAMPLE PROBLEM A logging company has a field with 84 trees in it. They have cut down 28 trees. How many trees have they left standing? 84 - 28 = ….. Number of trees there were. Number of trees that have been cut down. Number of trees that are left.
- 3. SAMPLE PROBLEM Step 1: Draw a number line and write in the total amount of trees on the right hand side of the number line. 84 - 28 = ….. Hint: Remember number lines always run from smallest to largest. 84
- 4. SAMPLE PROBLEM Step 2: Choose a tidy number which is close to 28 and subtract this. 20 is a tidy number but it’s not the closest tidy number to 28. 30 is a tidy number. This is the best choice. 84 - 28 = ….. 8454 Hint: When you subtract by a tidy number the ones digit doesn’t change. -20 -30
- 5. SAMPLE PROBLEM Step 3: We took away 30 but we only needed to take away 28. To fix this we must now jump back up 2. 84 - 28 = ….. 8454 -30 +2 56 Hint: You move down the number line (to the left) when subtracting because the numbers are getting smaller and to the right when adding because the numbers are getting bigger. That means 84 – 28 = 56
- 6. Now let’s try one together Andrew is carrying a tray with 63 eggs in it. He drops it and 27 break. How many eggs are not broken? 63 - ? = 27
- 7. Now let’s try one together Step 1: Draw a number line with your starting point. Do this now on a piece of paper. 63 - ? = 27
- 8. Now let’s try one together Step 2: Choose a tidy number to jump back. Remember this needs to be a tidy number which is very close to 27. Do this now. 63 - ? = 27
- 9. Now let’s try one together Step 3: Because we jumped back 30 we jumped a bit too far. Work out how much we need to jump back up the number line to fix this. Add this to your drawing now. 63 - ? = 27
- 10. Now let’s try one together Answer: What is the answer to our sample question? Write this in now. 63 - ? = 27
- 11. Now try these questions on your own. 1) 76 – 19 = ….. 2) 83 – 58 = …. 3) 67 – 38 = …. 4) 85 – 47 = …. 5) 58 – 29 = …. 6) 72 – 47 = …. 7) 93 – 39 = …. 8) 34 – 18 = …. 9) 64 – 28 = … 10) 75 – 37 = …
- 12. Only click again if you have completed all the questions on the previous slide and you are ready to see the answers. 1) 57 2) 25 3) 29 4) 38 5) 29 6) 25 7) 54 8) 16 9) 39 10) 38 Need some more practise? Try Pg51 of Teacher Tools Addition and Subtraction Book Numeracy resources