Unit Rates That Tell You Which Is Cheaper

Grab these first

• paper and pencil
• calculator (optional, for checking division)
• two similar grocery items from your pantry or fridge, such as two different boxes of cereal, two cans of beans, or two bottles of juice (choose ones with clear price tags and quantities that divide evenly into whole cents)

1. 1

   Explain the idea

   Unit rates make it easy to compare two deals that look different at first. A unit rate tells you the cost for one single unit, like the price per ounce or the price per mile. To find it, divide the total price by the number of units.

   Here is an example with two brands of pasta sauce. Brand A costs $3.60 for 24 ounces. Brand B costs $2.25 for 15 ounces. Which is cheaper per ounce?

   First find Brand A's unit rate: $3.60 ÷ 24 = $0.15 per ounce.

   Now Brand B: $2.25 ÷ 15 = $0.15 per ounce.

   They cost the same per ounce, so it is a tie.

   Try this one yourself. A 5-pound bag of apples costs $4.95. A 3-pound bag costs $3.15. Which bag gives you more apple for your money? Divide each price by the pounds to get the price per pound, then compare the two unit rates. The lower number wins.

2. 2

   Sit with Maya and read the concept explanation above out loud together. Pause after each example so she can follow the division steps and see how the unit rate helps you compare.

3. 3

   Ask her to explain in her own words why a lower unit rate means the better deal. Then work the apples example from the explanation together. Have her do the two divisions on paper and circle the cheaper rate.

4. 4

   Gather the materials listed below. Tell her you are going to turn your kitchen into a comparison shopping lab. You will look at two real products that seem similar but come in different sizes and prices.

5. 5

   Guide her through the activity step by step. For each product pair, she should write the two prices and quantities, calculate both unit rates (price per one unit), and decide which is cheaper. Remind her to keep prices in dollars with two decimal places.

6. 6

   After the activity, ask her these two questions: How did the unit rates make the choice clearer? Was there a time when the bigger package was not the better deal? Listen to her answers and praise clear thinking.

7. 7

   Wrap up by having her jot down one tip she would give a friend who wants to save money at the store. Keep the whole lesson light and end while she still feels successful.

8. 8

   Do this together

   Turn the lesson into a quick shopping comparison using things you already have at home. Pick two pairs of similar products (for example, a 12-ounce jar of peanut butter for $2.88 and an 18-ounce jar for $4.14, or two boxes of pasta). For each pair, Maya writes the price and the amount on paper. She then calculates the unit rate for each (price divided by the number of ounces, pounds, or whatever the unit is). She records both unit rates and circles the cheaper one. Do two or three pairs so she gets comfortable with the division and the comparison. If you have a runner in the house, you could also compare two sports drinks by price per fluid ounce. The goal is for her to see that the unit rate cuts through the confusion of different package sizes.