2) The rate for the service of a telephone company is given by the expression C (t) = 1.5t + 400, where t is the number of minutes consumed per month. a) Describe of
the written way how the rate works. b) How much will a person who consumes 300
minutes in a month? c) If a person paid a bill for $ 775, how many minutes did they consume
in the month?
Solution:
a) You pay $ 1.5 for each minute consumed, plus a flat charge of $ 400.
b) C (300) = 1.5 (300) + 400 = 450 + 400 = $ 850
c) Given that t is the number of minutes spoken, we have:
C (t) = 775 → 775 = 1.5t + 400
775 - 400 = 1.5t →
375
1.5
= t ↔ t = 250 minutes