Models & Applications: Monthly Cost

Question

The phone company Ringular 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. If a customer uses 190 minutes, the monthly cost will be $63. If the customer uses 760 minutes, the monthly cost will be $177.

A.) Find an equation in the form y = mx + b where x is the number of monthly minutes used and y is the total monthly cost of the Ringular plan.

y = ___________________

B.) If 845 minutes were used, the total cost will be ___________ dollars.

Answer 1

y = F + m, F is fixed constant, y and m are variables

63 = F + 190M where x = 190 monthly minutes used, y= $63 total cost, and F = monthly fee and M = cost per minute

177 = F + 760M

63= F + 190M

subtract to get

114 = 570M

M = 114/570 = .2 = 20 cents per minute

F = 63 -190(.2) = 63-38 = 25 dollars fixed monthly fee

y = 25 + 0.2x

y = 25 +.2(845) = 25 + 165 = $190 for 845 minutes