Question

Martina purchased a prepaid phone card for $15.00. Calls cost 5 cents a minute using this card. The credit, C (in dollars), left on the card after it is used for x minutes of calls is given by the following function.

C (x) = 15.00 -0.05x

How much credit is left on the card after Martina uses it for 20 minutes of calls?

Answer 1

The function is
C(x) = 15.00 - 0.05x

C is how many dollars are left after
x minutes.

So if she uses it for 20 minutes, input that into the x.

C(20) = 15.00 - 0.05(20)
C(20) = 15.00 - 1
C(20) = 14.00


After 20 minutes, there are $14.00 left on the card.