Set Up Shop with Algebra!

By Brigid Del Carmen

One way to make variables and expressions more concrete for middle school students is to use real-world examples. Using items around your house, create a “store” and set up expressions to represent the cost of the items. It takes just a few minutes to set up, but this activity will have lasting effects. Those once abstract and confusing variables and expressions will now represent real-world thinking – and real-world shopping!

What You Need:

• Sticky notes
• Black marker
• Household items, such as books, playing cards, paper clips, cucumbers, apples
• Paper and pencil
• Clipboards (optional)

What You Do:

(b) book = $10.00

(n) napkin = $.25

(y) playing cards = $1.00

(a) apple = $.90

(p) paper clips = $.10

(s) spoon = $2.50

(f) forks = $3.50

(w) water = $1.75

(d) soda can = $1.50

(c) cucumber = $3.50

2(10.00) + 3(3.50)

20.00 + 11.50

31.50

1. Set out several household items (1 of each) and label each with a variable and a price (on sticky notes). For example:
2. Begin the activity by explaining to your child that every time you are shopping, especially at the grocery store, you write expressions “in your head”. It’s really simple if you think of writing expressions as just writing out what you are thinking as you shop.
3. Explain how you would set up a simple expression to represent the cost of one item.
4. Say: “I want to buy 3 apples.
5. First, I set up an expression to represent the cost of the apples: 3a
6. Next, I calculate the cost of the apples by filling in the price of each apple: 3(.90) = $2.70
7. Now, demonstrate how you would set up an expression with 2 terms.
8. Say: “I want to buy 2 books and 3 forks.
9. First, I set up an expression to represent the cost of both items:
10. 2b + 3f
11. Next, I calculate the total cost of the items by filling in the price of each item:
12. Continue providing examples, each time adding another item. Once you feel your child has an understanding of the process, it’s time to send him shopping! Give your middle-schooler lists of items and the quantity for each. Ask him to set up expressions and calculate a total for each shopping list. Extend the activity by asking him to predict which list will be the most/least expensive before solving.

Tips:

Review by asking your child what each expression means. For example, 2f + 8s + 3p means: the cost of 2 forks, 8 spoons, and 3 paper clips.

Take your child to the grocery store. Give him a notepad and, as you shop, have him write expressions to represent the cost of what is in the cart. For example, if you are buying 4 cans of tomatoes, the expression is 4t. If each can costs $.80, he should evaluate the expression: 4(.80) = $3.20. Ask him to estimate the total cost of the items in your grocery cart before you check out. Challenge him to come as close to the actual total as possible.