Question

Jane has a pre-paid cell phone with Ringular. She can't remember the exact costs, but her plan has amonthly fee and a charge for each minute of calling time. In June she used 400 minutes and the costwas $147.00. In July she used 860 minutes and the cost was $285.00.aA) Express the monthly cost C as a function of 2, the number of minutes of calling time she used.Answer:

Answer 1

We can use a linear equation to represent this situation.

In this case the linear equation y= mx + b can be expressed as C(t) = mt + b ( m: slope of the line or the charge for each minute and b is the y-intercept or the monthly fee)

We have to find the slope of the line with the points (400, 147) and (860, 285)

`m=(y2-y1)/(x2-x1)=(285-147)/(860-400)=(138)/(460)=0.3`

Then, we can find the monthly fee replacing the slope and one of the points in the linear equation. Let us use the point (400,147).

147 = 0.3(400) + b

147 = 120 + b (Multiplying)

27 = b (Subtracting 120 from both sides of the equation)

The answer is C(t)= 0.3t + 27 (t in minutes)