Material
- Assortment of coloured bead bars.
- Golden (orange) bars of 10.
- Black and white bead stair.
- Assortment of subtraction beads.
Presentation
- Explain to the child about the subtraction beads-that we are going to lay out a colored snake as before-and put in these gray bead bars as well.
- When counting the snake, when we come to a gray bead bar, we are going to take away that number. (When laying out the snake, make sure there is a good quantity of positive beads before putting in a subtraction bar).
- The snake is counted-so far there are 3 golden tens and a black 9. A gray bar of 8. It is counted, and you say to the child ‘We are going to count back 8,’ and so on, we are left with one black bead. We lay out a black bead, and put the gray bar in this box and the black and white 9 in the stair.’ (The various bars must be kept separate from the bars not being used).
- Continue counting the snake, remarking that the snake is now getting big, and now getting small.
- We started off with a big, long snake, but when we had counted it and subtracted the gray bars, we were left with a small snake.
Note
Special care must be taken in working the subtraction snake so as to avoid mixing the 4 different kinds of beads. It will safeguard the work if, prior to counting, the boxes containing unwanted beads are closed and set safely aside. The box of golden tens remains open, however, as it is to supply an unknown quantity. Have two trays of boxes to contain positive and subtraction bars after they have been counted.Trouble must be taken to keep the white and black stair in proper sequence while the work is in progress. This will facilitate matters as the game is fairly complicated. After some time leave the child to lay out the snake for himself, but insist that he should have a good number of coloured bead bars at the beginning.
Direct aim
To familiarize the child with his subtraction tables.
Age of great interest
5 years plus.
Control of error
- To lay out a snake containing an equal number of positive and negative beads! Lay out the golden tens and black and white beads of the result.
- Sort out the beads (colored) used to make the original snake.
- Taking the negative beads, put the corresponding number of colored beads from the snake with them.
- The number of colored beads remaining should correspond to the number of the ‘golden’ snake.