Material
- The subtraction strip board is, in its size and number of squares, an exact replica of the addition strip board, the only difference being that a blue line divides the board vertically after the ninth square. The first nine squares are numbered in blue, and from 10 to 18 are in red.
- Accompanying the board are two sets of red and blue strips and one set of plain wooden strips (17).
Direct Aim
Memorization of essential subtraction combinations.
Control of Error
Chart 1.
Age of Great Interest
5½ to 6½ years.
Presentation: General Introduction.
- Explain to the child that the plain brown strips are to cover up the squares we don’t want. The number left is what we are concerned with.
- Lay out all the brown strips beside the board.
- Lay out the blue strips on the right side of the board.
- Take a short brown strip-covering (6) squares. What are we left with? The number 12.
- Let’s see how many numbers we can take from 12 leaving the answers in the blue numbers only.
- Take the blue strip of (5) and place it beside the brown strip. What have we left? 7. Is it in the blue number? Yes. So that is right.
- Continue with blue strips until you take strip 2: 12- 2=10 (that’s in the red numbers).
- Work using random numbers.
Exercise: [First exercise or Second Stage] Tables (subtraction)
Material
- Table of 1
Exercise
- Take longest brown strip, leaving 1 square; place ‘blue 1’
- So1-1=
- Table of 2: 2-2=0, 2-1=1
- Table of 16: 16-9=7, 16-8=8, 16-7=9
Control of Error
Is in control chart 1.
Method for writing out tables in sum book:
| 15 | 16 | 17 | 18 |
|---|---|---|---|
| 15-9=6 | 16-9=7 | 17-9=8 | 18-9=9 |
| 15-8=7 | 16-8=8 | 17-8=9 | |
| 15-7=8 | 16-7=9 | ||
| 15-6=9 |