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# Stamp Game Subtraction

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4. Decimal System
5. Stamp Game Subtraction

#### Material

Small wooden squares, all the same size:
Green squares with the symbol 1.
Blue squares with the symbol 10.
Red squares with the symbol 100.
Some green squares with the symbol 1000.
Skittles (for division): 9 green, 9 blue, 9 red and 1 large green.
Some small discs in green, blue, and red.
A compartmented box for all the above.
A tray with squared paper, pencil and ruler.
Small strips of paper (green or another color).

#### Presentation

##### Static Subtraction
1. Invite the child to the lesson.
2. Show him the small dish of green paper slips and ask him to bring them to a table.
3. Ask him to bring two papers, two underlays, and two pencils on a tray.
4. Ask him to bring the stamp game box.
5. Write a number such as 5874, ask the child to write it too.
6. Wait for the child to make the number with the stamps.
7. “I’m going to write the number we take away on this green sleep.”
8. Write another number, this time on the colored slip, such as 2621.
9. Place the green sleep to the right.
10. Rewrite 2621 on the other paper, ask the child to write it too.
11. “We’re going to take away this number. How many units are in this number? Right, just one.”
12. Move a unit stamp below the green slip.
13. “How many tens? Yes, two.”
14. Move two ten stamps below the green slip, and so on with the other categories, into columns.
15. Once all categories on the green slip have been placed below the slip, ask the child to count what remains of the original number.
16. One category at a time, the child should count the stamps and write the number of that category onto the paper, starting with the units.
18. “Yes, 3253. We did subtraction!”
19. “There is nothing here that says we did subtraction, so here is a symbol, that means subtract. We call it minus.”
20. “5874 minus 2621 equals 3253.”
##### Dynamic Subtraction
1. Repeat the process the same as before, but only use only paper, one pencil, one underlay on a tray.
2. Dictate a number such as 7253, and ask the child to write it.
3. Wait for the child to make the number with the stamps.
4. Dictate another number such as 4629, and ask the child to write it.
5. If necessary, remind the child to write the minus sign.
6. “We need to take away nine 1’s, but there are only three 1’s here.”
7. “We can exchange one 10 stamp for ten 1 stamps!”
8. Wait for the child to complete this exchange and make sure he subtracts the correct number of stamps away, in this case nine, and places them to the right side of the table.
9. Continue this process for all the other categories, exchanging when necessary.
10. “7253 minus 4629 equals 2624.”

#### Exercises

Child works independently.

#### Purpose

To reinforce what was learned with the collective exercises by means of individual work.
Further experience with place value.
To show how to write a problem.

#### Control of Error

You can show the child how to check by reversing the process; adding the subtracted amount back to the answer to form the original.

#### Age

5 to 5 1/2

We only use the green paper slips 3 to 5 times, as it isn’t necessary after that. The green slip is used at first because the children were confused about what was happening, so the green slip was introduced to help ease their confusion.