Math Investigations

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Chapter 3

Part 1: For the problem in the Teacher's Edition, page 44

Discuss with the students ways they might find out the cost of one cup of lemonade without dividing. You might want to give them a hint by pointing out that the difference between the number of cups sold Monday and the number of cups sold Thursday is one cup.

Some students might benefit from using play money coins to find different ways to use coins to make 50¢, the cost of one cup of lemonade. When students have finished doing this, have them share the ways they used coins to make 50¢. See how many different ways the class can find. Provide students with the Problem Worksheet (PDF file).

One cup of lemonade costs 50¢.

Possible ways to find the cost without dividing:

Subtract the cost of 18 cups of lemonade from the cost of 19 cups of lemonade or the cost of 17 cups of lemonade from the cost of 18 cups of lemonade.

The Ways to Make 50¢, the Cost of One Cup of Lemonade (with at least one quarter and no pennies):

  • 2 quarters
  • 1 quarter, 5 nickels
  • 1 quarter, 1 dime, 3 nickels
  • 1 quarter, 2 dimes, 1 nickel

Part 1: Be an Investigator

A good time to do this investigation is after Lesson 1 on the value of money.

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 students in groups of two to four students to work on the investigation. Provide students with the Description of Investigation and Student Report (PDF file).

Doing the Investigation

Discuss the choices students made and how they made their choice. If not brought out as part of the discussion lead students to conclude that Tuesday would probably be the best day to close since the fewest cups of lemonade were sold on Tuesday during the four-week period.

Student Report

The report gives students an opportunity to write about why they made the choice they made, thus communicating about mathematics.

Extending the Investigation

Have students tell which days they would be open if they could only be open three weekdays. Have them tell why they made their choice.

Houghton Mifflin Math Grade 3