Question

The monthly cost (in dollars) of a long-distance phone plan is a linear function of the total calling time (in minutes). The monthly cost for 39 minutes of calls is 18.45 and the monthly cost for 56 minutes is $20.66. What is the monthly cost for 50 minutes of calls?

Answer 1

Explanation:

We can use the two data points given to find the equation of the line, which gives the monthly cost (y) in terms of the calling time in minutes (x).

First, we can find the slope of the line:

slope = (change in y) / (change in x)

slope = (20.66 - 18.45) / (56 - 39)

slope = 0.219

Next, we can use one of the data points and the slope to find the y-intercept (b). Let's use the data point (39, 18.45):

y - y1 = m(x - x1)

y - 18.45 = 0.219(x - 39)

y - 18.45 = 0.219x - 8.541

y = 0.219x + 9.909

So the equation for the monthly cost is y = 0.219x + 9.909.

To find the monthly cost for 50 minutes of calls, we plug in x = 50:

y = 0.219(50) + 9.909

y ≈ $21.44

Therefore, the monthly cost for 50 minutes of calls is approximately $21.44.