NEGATIVE SNAKE GAME
To familiarize the child with subtraction combinations.
Indirect preparation for algebra as from time to time equal quantities of the opposite sign cancel each other out, as in algebraic formulae.
Boxes containing: colored bead bars (about 3 of each);
20 golden ten bars;
black and white stair;
negative bead stairs;
one box or little tray to contain the beads that have been counted;
small notched card;
green felt mat.
The child is shown how to check his answer with the control.
5.5 – 6 years
Presentation: (After the child has mastered the positive snake game.)
At a table lay out the materials as in the positive snake game.
Introduce the grey bead stair and say, “These are the negative bead bars. They tell us how many to take away.”
The child identifies the grey bead bars by counting.
The child builds a snake as before and places three or four grey bead bars interspersed among the colored bead bars.
(Note: in placing the grey bead bars, the snake should not go down to zero or into a minus number.)
Proceed to count as before.
When a grey bead bar is reached, in order to take away, count back that number of beads.
Count back on only black and white bead bars or golden bead bars.
Before counting back, any colored bead bars (less than 10) to the left of the grey bar must be changed into one black and white bead bar.
To count back –
The child counts the beads on the grey bar.
Then counts back into the black and white and/or golden beads, counting from right to left.
Mark with the notched card.
Count any remaining beads on the left side of the notched card and represent this remainder with the corresponding black and white bead bar.
Place the grey bead bar into the box with the other counted colored bead bars.
Replace the black and white bead bar into the stair.
Replace the golden bead bar into its box.
Rejoin the snake and note that it is getting shorter.
To check –
Arrange the golden snake and colored bead bars as before.
Arrange the grey bead bars vertically to the right of the colored bead bars in diminishing order.
Note: The colored bead bars represent the minuend, the grey beads represent the subtrahend and the golden bead bars represent the difference.
Match the colored bead bars to the golden and grey bead bars changing as necessary.
Exercise: As in the presentation.
Exercise 2: Isolating subtraction –
Proceed as above.
When the child has counted back and (at a later stage) found the remainder, pull down all the bead bars involved in the counting back process to the bottom of the mat.
Arrange the bead bars horizontally, so that the bead bars counted back on, match the grey bar and the black and white remainder.
Note the quantity of the golden bead bar and/or the black and white bead bar, ie. 10 and 4 make 14.
Note the quantity of the grey bead bar and the remainder, ie. 7 and 7 make 14.
“So 14 (pick up golden bead bar and/or black and white bead bar) take away 7 (pick up grey bead bar) is 7 (leave remaining black and white bar on the table).”
Place the bead bars in your hand in their respective places as before.
Place the remaining black and white bead bar back into the snake and rejoin the snake.
Continue in the same manner.
Check as in the presentation.