Math Investigations

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Chapter 18

Part 1: For the problem in the Teacher's Edition, page 460

Provide your students with a copy of the Problem Worksheet (PDF file).

Have the students share their methods of solving the problem. One method is to take half of the price of each doll and then add to find the total cost of the dolls on sale. Another method is to add to find the total price and then find half of that sum to find the sales price. Make sure students realize that they get the same answer either way. Look at any other methods students suggest, and have the class analyze them to see if they work.

Answer:
$1,570
One way to solve: Find one half of each price. Then add.
Another way to solve: Add the prices. Find one half of the total.

Part 2: Be an Investigator

A good time to do this investigation is after Lesson 8 on sales tax and discounts.

Introducing the Investigation

Introduce the investigation by reading aloud the assignment at the top of the first page of the Description of Investigation and Student Report (PDF file), by having one of your students read aloud the assignment, or by having the students read the assignment individually.

Put the students in groups of two to four to work on the investigation.

Doing the Investigation

Have the students share their strategies for solving the problem. Discuss the fact that you need to do some calculating to figure out which store offers the better deal for an item with a given regular price. In this case, for some items you will save more money by going to Pete's, and for other items you will save more money by going to Sue's.

Answers:

Item A
Regular Cost: $10
Pete's Sale Cost: $8 ($10 − $2 = $8)
Sue's Sale Cost: $9 (10% of $10 is $1. $10 − $1 = $9)
You save more money by buying the item at Pete's Hardware Store.

Item B
Regular Cost: $50
Pete's Sale Cost: $48 ($50 − $2 = $48)
Sue's Sale Cost: $45 (10% of $50 is $5. $50 − $5 = $45)
You save more money by buying the item at Sue's Hardware Store.

Student Report

The report gives the students an opportunity to tell which store they chose for each item and why, thus communicating about mathematics.

Extending the Investigation

Have the students figure out what the regular price of an item would be to have the same sales price at both stores. They'll discover that if the regular price of the item is $20, the sales price will be $18 at both stores. Discuss the meaning of this with the students. If the regular price of an item is less than $20, it is better to buy it at Pete's. If the regular price of an item is more than $20, it is better to buy it at Sue's.


Houghton Mifflin Math Grade 6