Subtraction Snake Game
Materials:
Green felt underlay the size of the table
Box of golden bars of 10
Box with colored short bead stairs
Box with 1 black and white bead stair
Box with gray bead bars (several sets1-9)
Notched marker
Tray
Purposes:
The first practice in memorization of the essential subtraction combinations.
Indirect preparation for algebra (equal quantities of opposite signs cancel each other).
Age: 5
Preparation:
The child has done subtraction with the Decimal System.
The child has worked with the Addition Snake Game.
Presentation 1: Shrinking the Snake
Invite the child to the lesson, to bring and open the underlay as the guide brings the materials
Explain this is similar to the other Snake Game.
Ask the child to build the remainder stair on the left side of the mat.
Open each box and place the lid beneath.
Introduce the gray bars and select a few for the child to count.
Invite the child to build a long snake.
At halfway through the building of the snake, begin alternating gray bead and a colored bead.
Close the gray and green boxes
Explain it will change to a golden snake, but it will get smaller.
Let the child count and exchange until the first gray bead.
Explain it is a takeaway bead and tells us to count back to take away.
Count the gray bead and then count back that many beads (starting at the bead bar prior to the gray bead), place the counter, and place a remainder. Remove counted beads and gray bead to the box holding the counted colored beads and remainder bead back to the stair. If a ten is broken-place the remainder bead and put the ten in the ten box.
Move the rest of the snake to the left.
Repeat. If there is a random colored bead at the end, exchange it for a remainder bead bar.
When the child is done marvel at its length. “It used to be so long and not it is so short!” (At some point show them a snake that completely disappears)
Note: The child needs time to practice this presentation before moving on.
Presentation 2: Verification
When the child is through counting the snake, line up the tens and the remainder on the left side of the mat
Sort out the counted beads: Colored beads ordered 9-1 oriented vertically on the right lower corner and the gray beads sorted 9-1 bars oriented vertically above.
Explain you will match the gray bead bars to the colorful beads.
Pull one to the top center of the mat and find the colored bead to match
Repeat pairing them moving to the right
If you do not have the match or cannot combine bars to make a match, A colored bead can be exchanged evenly for a bead from the green box.
After the grays are matched, match the rest of the colored beads to the ten bars in the same manner as in the Addition Snake Game Verification 1.
Presentation 3: Counting 2 by 2
Invite the child and set up the stair and the snake as in Presentation 1
Pull down the first two bars and have the child count and make exchange and place remainder.
Place gold bead back into the snake, move the remainder to the left and pull down the next bead. Continue in this way.
When you get to a gray bead, pull it down, count it and count backward, place remainder. Put gray and colored bead in the box. Shrink the snake and continue.
If there are not enough to take away, pull down the last ten in the snake and use it in addition to the beads already pulled down. Count, place remainder. The gold bar will go to the gold box. (Subtracting always toward the left)
Invite the child to do the verification
Control of Error: The verification process
Pedagogical Notes:
Emphasize that the first part of the snake is constructed with colored bead bars so there is enough to take away from once they get to the gray subtraction beads.
The gray and color beads cancel each other out.
This offers the child a sensorial experience of the process of subtraction