Note: As in the special cases for addition, these exercises are done after the child has already done much work with the previous exercises.
…subtraction combination booklet
…large sheet of paper or chart,
…red and black pens
…special combination cards
The teacher opens to a page, in the booklet. When you do these combinations, what do you do? calculate the difference.
As before the teacher writes the tile on the chart, gives an example and reads. In all of the other cases, the special case is set up first in the combination booklet or on a sheet of paper, and the child identifies the missing part. Then the special case is added to the chart.
0- Calculating the Difference
16 9 = ? (If from 16, I take away 9, what will be left?)
1- Calculating the Subtrahend
16 ? = 7 (From 16 I have taken away a certain number, and 7 is left. How much did I take away?
2- Calculating the Minuend
? 9 = 7 (From a certain number I have taken away 9, and 7 is left. What was that number?
3- Inverse of Case Zero – Calculating the Difference
? = 16 - 9 (What will be left if from 16 I take 9?)
4- Inverse of the 1st Case- Calculating the Subtrahend
7 = 16 - ? (7 is the remainder when from 16 I take away what number?)
5- Inverse of the 2nd Case- Calculating the Minuend
7 = ? - 9 (7 is the remainder when from a certain number I take away 9. What is that number?)
6- Calculating the Minuend and the Subtrahend
7 = ? - ? (7 is the remainder when from a certain number I take away another number. What is the first number, and what is the second number?)
The teacher passes out the special combination cards. Each child reads the combination, states what part is missing and which case it is. (referring to the chart)
The child works with the special combination cards as before: drawing one and computing it, then writing the equation in his notebook with the answer in red.
Aims: further memorization of subtraction combinations
reinforcement and understanding of the concept
Notes: This activity develops the ability to work with the same combination under different conditions and from various points of view, thus creating flexibility in the child’s mind. Here, also, we see the close relationship between addition and subtraction .