A phone company has a monthly cellular plan where a customer pays a flat monthly fee and then a certain amount of money per minute used on the phone.

Question

 If a customer uses 330 minutes, the monthly cost will be $51.50. If the customer uses 740 minutes, the monthly cost will be $72.

(a) Find a linear equation for y, the monthly cost in dollars, of the cell plan as a function of x, the number of monthly minutes used.

y = 

(b) Interpret the slope and y-intercept of the equation.

The  ---Select y-intercept or slope--- is the $  flat monthly fee, and the  ---Select y-intercept or slope--- is the $  fee for each additional minute used.

(c) Use your equation to find the total monthly cost if 694 minutes are used.

$ 

Answer 1

(330, 51.50)

(740, 72)

a line through those two points has slope = (72-51.5)/740-330) = 20.5/410 = 1/20

C = (1/20)M + F where M= number of minutes and F = the monthly fee, to solve for F plug in

either point

72 = (1/20)740 + F

f = 72 - 37 = $35 monthly fee

y=.05M + 35 is a linear equation giving the cost as sum of the monthly fee plus cost of minutes used

the y intercept is the monthly fee = $35

the slope is the cost for one minute used

y =.05(694) + 35 = 34.7+35 = $69.70 for 694 minutes

You knew it would be a little less than $72