Subtraction Snake Game


Materials: same materials as for previous snake games:
…box of colored bead bars 1-9
…box of ten bars
…box of black and white reminder bars (place holders)
…also box, with 9 compartments, for gray bead bars 1-9
(for bars of 6-9, there is a small space or color change after the fifth bead to facilitate counting)

As before, a snake is made, though this time we add to these colored bead bars, some gray bead bars. (Note: before the first gray bar appears, several colored bead bars should appear to create a large minuend) As before we begin counting, using the black and white reminder bead bars. When we come to a gray bar, we must subtract. The preceding black and white bead bar and the gray bar are isolated. 8 ­ 4 = 4 The 4 black bar is placed in the box cover with the other original colored beads.
Counting continues as usual. The next two bead bars are isolated: black 3 and gray 7. This gray bar means I must subtract. 3 ­ 7 is impossible; therefore I take one ten bar (from the snake’s new skin) and place it beside the 3 to make 13. 13 ­ 7 = 6. The black and white 6 is placed in the snake; the black 3 is placed with the other reminder bars; the ten bar is placed back in the box with the other ten bars; the gray 7 is placed in the box cover with the other original colored bead bars.
When the counting is finished, the gold bead bars (and reminder bar) are counted to find the result.

Control of Error: In the box cover are colored bead bars and gray bead bars mixed. First, these are separated into two groups, lain in chronological order. A gray bar is placed with its equivalent colored bar. Two colored bars may be combined to match a gray bar, or vice versa. When all of the gray bars have been matched; the colored bars are paired to be matched with ten bars as usual . When all of the bars have been matched, we know the counting was done correctly.

Direct Aim: to memorize subtraction

Indirect Aim: to prepare for algebra: positive and negative numbers


a. Passage From Chart I to Chart II

…Chart II (the numbers in pink function as the minuend; the blue as the subtrahend)
…combination cards
…Chart I

The child fishes for a combination, i.e. 9 ­ 2 =___, reads it and writes it down on his paper. A finger is placed on 9 on the pink strip on the chart.; another finger is placed on 2 on the blue strip. Where the two fingers meet, we find the difference. This is recorded on the paper. The child continues his work in this way, and when finished, he controls with Chart I.


b. The Bingo Game of Subtraction (using Chart III)

…Chart III and box of corresponding tiles
…combination cards
…Chart I (for control of combinations)
…Chart II (for control of placement of the tiles)

A. Exercise: 
The tiles are randomly arranged face up on the table. The child fishes for a combination, thinks of the answer, and finds the corresponding tile. After the minuend (pink) and subtrahend (blue) have been established on the chart, the child is able to find the place for the tile. He writes the equation on his paper and continues.

Control of Error: Charts I and II

B. Exercise: 
All of the tiles are in the box (or in a sack). The child fishes for a tile, and thinks, what could this be the remainder of? He thinks of a combination and writes it down, i.e.
7 = 14 ­ 7. He puts the tile in its place. He continues in this way, then controls his work.

C. Exercise: 
The tiles are arranged on the table in common stacks. The child chooses one stack and thinks of combinations which will yield this difference. He writes down the combination, finds the place on the chart, and so on, continuing until he has finished the stack.
When all of the stacks are arranged in order in a row, what form do they make? a rectangle or parallelopiped.

Group Games
1. The teacher, or a child functioning as the teacher, fishes for a combination and reads it. One of the children guess the difference.

2. The teacher fishes for a tile and the children offer combinations which give that result, until all are given.

Aim: (of all of exercises,) to memorize subtraction combinations

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