For example, for the toy giraffe you could write the label as
(g) = $.50 and for the toy boat you could use (b) = $.30. At this point, they don’t have to have realistic prices. It’s more important to give students simple numbers to work with.
Make sure you use unique variables for all the items.
Next, explain to the students that as you’re shopping you calculate the expressions in your head or on a notepad. You don’t want to overspend!
For example, if you wanted to buy 3 toy giraffes you would think “3g is the same as 3(.50) = $1.50.”
At the beginning, have them write expressions for the different items. Tell them you want to buy 4 toy turtles. If the label on the turtles says
(t) = $.25 then 4 turtles can be represented by 4(t) or 4t.
Once they’ve practiced this for a while it’s time to ask them how they would write an expression to show 2 toy giraffes and 4 toy boats.
They should be able to tell you 2g + 4b and figure out the price as
2 (.50) + 4 (.30) = 1.00 + 1.20 = $2.20.
This time, divide the class into pairs and give them some play money to spend–$5.00 or $10.00 might be a good budget. Tell them that their goal is to buy as many items as possible and have the least amount left over from their budget. They must buy at least 4 different items, they can buy more, but they must buy at least 4. They can also buy more than one unit of an item.
Once they have made their final decisions about what to buy, they will need to write an expression for you to check.
(b) = $.30 (toy boat)
(g) = $.50 (toy giraffe)
(t) = $.25 (toy turtle)
(d) = $.45 (toy doll)
With a budget of $10.00 they could buy:
5b + 8g + 6t + 6d =
5 (.30) + 8 (.50) + 6 (.25) + 6 (.45) =
1.50 + 4.00 + 1.50 + 2.70 = $9.70
If they buy one more toy boat, they won’t have any money left at all!
You can also reverse the game and have them buy any combination of four items to ensure they spend the least amount of their budget as possible!