Explain that for partial differences subtraction you put the numbers one under the other. Then you can subtract them from one another by working from left to right. So you start with calculating the hundreds numbers. You subtract them from each other. Then you subtract the tens numbers and finally the ones numbers. With subtracting the ones values it can happen that you come up short. In that case you write a minus sign. You put all these answers in the diagram and write the intermediate differences are. You then add all of the answers together, besides the ones value if you were short. You subtract that number. Then you will arrive at your final answer. You put this final answer at the bottom of the diagram. Next, there is a problem in a diagram for which different rows are marked in yellow. Ask the students if they know which intermediate difference belongs in each colored row. This is how you can check whether students know which steps they must take. After this, have the students solve a few problems using partial differences. Then you explain that you can also come up short in the tens numbers. In that case, you also write a minus sign. Then practice partial differences further with two problems, for which one the diagram is already filled in and the other must still be filled in.
Check whether the students can subtract using partial differences with the following questions/exercise:
- Why is it useful to be able to subtract using partial differences?
- What do the letters H T O mean?
- Where do you always start when you calculate partial differences?
- Solve these using partial differences: 856 - 92 and 936 - 473