Question

A long-distance calling plan charges 99 cents for any call up to 20 minutes in length and 7 cents for each additional

minute.
(a)Write a function to represent the cost, C, of a call as a function of its length tin minutes.
b)State the domain and range of the function.
c)Determine the cost of a call that lasts 12minutes.
(d)Determine the cost of a call that lasts 1 hour.

Answer 1

a) Let's call the length of a call "t" (in minutes). The cost of a call can be represented as follows:

C(t) = 0.99 if t <= 20

C(t) = 0.99 + 0.07(t - 20) if t > 20

b) The domain of the function is all non-negative real numbers (t >= 0), since a call can have any non-negative length in minutes. The range of the function is all non-negative real numbers, since the cost of a call can never be negative.

c) If a call lasts 12 minutes, then the cost would be 0.99:

C(12) = 0.99

d) If a call lasts 1 hour (60 minutes), then the cost would be:

C(60) = 0.99 + 0.07(60 - 20) = 0.99 + 0.07(40) = 0.99 + 2.80 = 3.79

Explanation: