The document describes someone buying a stamp for $15, selling it for $20, buying it back for $25, and selling it again for $30. To solve how much money was made or lost, it defines x as profit and calculates x = -15 + 20 - 25 + 30 = $10, so they made $10 by buying and selling the stamp.

1. Acting
it Out
A Problem-Solving Strategy

3. You buy a stamp for $15

4. You buy a stamp for $15
You then sell it for $20

5. You buy a stamp for $15
You then sell it for $20
You then buy it back for $25

6. You buy a stamp for $15
You then sell it for $20
You then buy it back for $25
You then sell it again for $30

7. How much
money did you
make or lose
in buying
this stamp?

9. How much
money did you
make or lose
in buying
this stamp?

10. How much You buy a stamp for $15
money did you You then sell it for $20
make or lose
in buying You then buy it back for $25
this stamp? You then sell it again for $30

11. How much You buy a stamp for $15
money did you You then sell it for $20
make or lose
in buying You then buy it back for $25
this stamp? You then sell it again for $30
Acting it
Out

12. v ie s
e m o
t o th
t ’s go
L e

13. v ie s
e m o
t o th
t ’s go
L e

14. How much You buy a stamp for $15
money did you You then sell it for $20
make or lose
in buying You then buy it back for $25
this stamp? You then sell it again for $30
Acting it Out

15. How much You buy a stamp for $15
money did you You then sell it for $20
make or lose
in buying You then buy it back for $25
this stamp? You then sell it again for $30
Acting it Out
Let x = profit

16. How much You buy a stamp for $15
money did you You then sell it for $20
make or lose
in buying You then buy it back for $25
this stamp? You then sell it again for $30
Acting it Out
Let x = profit
x = -15 + 20 - 25 + 30

17. How much You buy a stamp for $15
money did you You then sell it for $20
make or lose
in buying You then buy it back for $25
this stamp? You then sell it again for $30
Acting it Out
Let x = profit
x = -15 + 20 - 25 + 30
x = 10

18. How much You buy a stamp for $15
money did you You then sell it for $20
make or lose
in buying You then buy it back for $25
this stamp? You then sell it again for $30
Acting it Out
Units: $ Let x = profit
x = -15 + 20 - 25 + 30
x = 10

19. How much You buy a stamp for $15
money did you You then sell it for $20
make or lose
in buying You then buy it back for $25
this stamp? You then sell it again for $30
Acting it Out
Units: $ Let x = profit
x = -15 + 20 - 25 + 30
x = 10
You will make $10.