The Price is Right

(c) Lynette Long

Compare prices when one price is in metric units and the other is English units.

Materials

• Newspaper
• Scissors
• Paper
• Pencil
• Calculator

Procedure

1. Cut out ads from the newspaper for soft drinks. The ads should have the prices included.
2. Glue each ad on a white sheet of paper.
3. Compute the price of each product per ounce and per liter. Write your computations and results on the back of each white sheet of paper.
4. Put the ads with the soft drinks face up in a row on the table. Ask your Mom or Dad to put the products in order from least expensive to most expensive. In order to compare prices products have to be in the same units.
5. How many products did you Mom or Dad get correct?

Tips and Tricks

Suppose you saw an ad for a liter of Coke for $1.00 and you saw another ad for six cans of Coke for $2.40. Which is cheaper? A liter of Coke is in metric measurement and six cans of coke are measured in ounces, which is English measurement. You have to change both products to English or metric measurements in order to compare them.

Compute the price of both products in metrics measurements first. Change both products to liters first.

The liter of coke is 1.00 per liter.

Each of the six cans of coke contains 12 fluid ounces of coke for a total of 72 ounces. There are 8 fluid ounces in a cup, 16 fluid ounces in a pint and 32 fluid ounces in a quart. To change six cans of Coke to liters, you first have to change it to quarts and then to liters. Seventy-two ounces is the same as 72/32 or 2.25 quarts. One quart is .95 liters so multiply 2.25(.95) to find out how many liters of coke in 72 ounces. The result is 2.1375 liters. Divide the cost of the six pack of coke, $2.40 by the number of liters, to find out cost per liter. The six pack of coke is $1.12 per liter, so it is more expensive.

What happens if you compare the price of the Coke per ounce?

Change the liter of Coke to ounces. To change it to ounces, you first have to change it to quarts and then to ounces. One liter of Coke is 1.06 quarts. Since a quart contains 32 ounces multiply 32 times 1.06 to find the number of ounces in a single liter. There 33.92 ounces in a liter. Since the liter of Coke cost $1.00 divide 1.00 by 33.92 to determine the price per ounce. $1.00/33.92 =.029. The coke in the liter bottle costs 3cents an ounce.

The six-pack of coke contains 72 ounces and costs $2.40. To compute the cost per ounce, divide $2.40 by 72, which is .033. The cost of the Coke in cans is also 3 cents per ounce. Although both products cost 3 cents an ounce, the Coke in the cans in slightly more than three cents an ounce.

(This activity is reprinted with permission from: Long, Lynette, The Magical Math Series, Measurement Mania, John Wiley & Sons, New York, 2000.)