A long distance telephone company advertised the rates of 5 minutes for 85 cents, & 10 minutes for $1.10.?

Question

Use a linear equation to find the cost of 25 minute phone call.

Answer 1

$0.05/min + $0.60
1.25 + 0.6 = $1.85

Answer 2

2

Answer 3

Since we are told the expression is linear, find the slope in dollars/minute:

(1.1 - 0.85)/(10 - 5) = $0.05/min.

So the rate must be 5 cents per minute. Now you could either find a general equation by finding the cost of a 0-minute phone call, or you could find the cost of a 25-minute call directly by adding the additional cost for 15 minutes to the cost of the 10-minute call:

c(25) = c(10) + (25 - 10)*0.05
c(25) = 1.10 + 15*0.05
c(25) = $1.85

A 25-minute call will cost $1.85.