Course 1 Unit 3

Lesson 3 Investigation 3-Making Comparisons

Name: ______

Date: ______Pd: ______

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1. For both companies, the monthly charge is a function of the number of calls made.

  1. Write linear equations giving the relations between number of calls and monthly charge for each company.
  • Equation for Regional Exchange: ______
  • Equation for General Telephone: ______
  1. Compare the monthly charges by each company for 80 calls. Show your work.
  • Regional Exchange:
  • General Telephone:
  1. How many calls could you make in a month for $30 under the pricing plans of the two companies? Show your work.
  • Regional Exchange:
  • General Telephone:
  1. For what number of calls is Regional Exchange more economical?
  • For what number of calls is General Telephone more economical?

e. Which plan would cost less for the way your family uses the telephone?

2. To compare the price of service from the two telephone companies, the key problem is

finding the number of calls for which these two rules give the same monthly charge. That means finding a value of x for which each rule gives the same y.

  1. How could you use tables and graphs to find the number of calls for which the two telephone companies have the same monthly charge?
  1. When one class discussed their methods for comparing the price of the service from the two companies, they concluded, “All we have to do is solve the equation

8 + 0.15x = 14 + 0.10x.” Is this correct?

  1. Solve the equation:

Math ToolKit: Understand what is meant by a system of linear equation and solving the system.

Regional Exchange: y = 8 + 0.15x

General Telephone: y = 14 + 0.10x

  1. How is the solution to a system of equations shown in graphs?
  • How is the solution to a system of equations shown in tables?
  1. Solve each system of linear equations using graphs, tables, or symbolic reasoning. Check each answer by substituting the solution values for x and y back in the original equations.

a. b.

c. d.

Checkpoint:

In solving a system of linear equations like y = 5x + 8 and y = -3x + 14, be able to answer the following questions:

a) What is the objective?

b) How could the solution be found on a graph of the two equations?

c) How could the solution be found in a table of (x, y) value for both equations?

d) How could the solution be found using reasoning with the symbolic forms

themselves?

e) What patterns in the tables, graphs, and equations of a system will indicate that there

is no pair of values for x and y that satisfies both equations?

Course 1 Unit 3 Lesson 3 Investigation 3Page 1 of 5