Explain that for partial differences you put the numbers one under another. Then you can subtract them by working from left to right. So you start by calculating the hundreds values. You subtract these from each other. Then you subtract the tens numbers from each other, and then the ones values. You put all these answers in the diagram and you state what the intermediate problems are. If you add up the numbers in the diagram, you find the final answer. You put this final answer at the bottom of the diagram. Next, there is a problem in a diagram for which different lines are marked in yellow. As the students if they know which intermediate problem belongs in each of the colored rows. This is how you can check whether students know what steps they must take in solving such a problem. After this, you show a diagram for which the intermediate steps must be filled in. Have the students write these numbers down and hold them up so that you can check them. Then remove the cover to show what the answer is. Next, practice more partial differences with two problems, of which one has the diagram already filled in and the other must still be filled in.
Check whether the students can calculate partial differences using the following questions/exercise:
- Why is it useful to be able to calculate partial differences?
- What do the letters H T O mean?
- Where do you always start when you solve a partial difference?
- Solve these problems as partial differences: 567 - 36 and 484 - 362