Question

A telephone company offers a monthly cellular phone plan for $19.99. It includes 350 anytime minutes plus $0.25 per minute for additional minutes. The following function is used to compute the monthly cost for a​ subscriber, where x is the number of anytime minutes used.

C(x)= 19.99 if 0 350
Compute the monthly cost of the cellular phone for use of the following anytime minutes.
​(a) 225 ​(b) 420 ​(c)

Answer 1

(a) $19.99

(b) $37.49

Explanation:

For up to 350 minutes:

C(x) = 19.99

For more than 350 minutes:

C(x) = 19.99 + 0.25(x - 350) for more than 350 minutes

C(x) = 19.99 + 0.25x - 87.5

C(x) = 0.25x - 67.51

(a) x = 225

Use the first equation.

C(x) = 19.99

C(225) = 19.99

Answer: $19.99

(b) x = 420

Use the second equation.

C(x) = 0.25x - 67.51

C(420) = 0.25(420) - 67.51

C(420) = 37.49

Answer: $37.49