Question

Define a variable, write an equation, and solve.

One cell phone plan costs $39.95 per month. The first 500 minutes of usage are free. Each minute thereafter costs $.35. Write a rule that describes the total monthly cost as a function of the number of minutes of usage (over 500 minutes). Then find the number of minutes of usage over 500 minutes for a bill of $69.70.

Answer 1

• c(m) = 39.95 +0.35m
• 85 minutes over 500

Explanation:

Let m represent the number of minutes used over 500. Then the cost of the cell phone plan is ...

c(m) = 39.95 +0.35m

__

For a cost of 69.70, the number of excess minutes can be found by solving ...

69.70 = 39.95 +0.35m

29.75 = 0.35m . . . . . . . . . subtract 39.95

29.75/0.35 = m = 85 . . . . divide by the coefficient of m

The number of minutes of usage over 500 is 85.