## Friday, July 29, 2011

### Price Per Item Calculations

Yesterday I introduced the subject of money in the elementary math class. Talking about buying things is a fairly popular part of math class, although our conversations should lean toward thrift, not wild abandon.

We have to be careful in the curriculum not to use any brand names or illustrations that might imply we are endorsing a certain product. And lately, we have had to remove all references to sugary foods.

Here's a typical lesson on unit pricing. This requires higher order problem solving skills. [click on the image to enlarge it]

We have co-mingled prices given "by the ounce" and "by the pound" to give kids practice in unit conversions. They should understand the relationship of ounces to pounds. They must know the number of ounces in a pound. They need to do a division problem to learn the cents per ounce.

In Clarissa's birthday roller skating problem, we provided the beginning of a story and kids are asked to finish the story, then create several of their own problems. We have provided teachers with a sample problem and how to find the answer.

This is a relatively complex problem where data is given in the narrative portion of the story. One tricky part is for the student to remember that Clarissa must pay for admission too, in addition to her 14 friends.

As the roller rink is giving a discount of one dollar per person, you must remember to deduct that from the total of the entrance fees. In this example, we took the dollar off of the two prices (\$10 becomes \$9; \$15 becomes \$14) but we could just as easily have waited until the end and subtracted \$15 (\$1 x 15 admissions).

In most comparison shopping situations, you are in a store, faced with choices, and must make a decision relatively quickly. The ability to calculate these types of prices in your head is a useful skill.

Once in a while you have time to analyze things more carefully. This earlier blog on the cost of a cup of tea is an example of a complex cost-per-unit problem solved over the course of an evening or two.

This challenge interested me, because the tea was from the same source and of the same type. Creative study of the purchasing options indicated we could cut the price from 58 cents to 16 cents per cup, for the same tea!