Cell phone company A charges $40 a month, with 500 free minutes and $0.10 a minute after that. Cell phone company B charges $25 a month and all minutes cost $0.05.

Question

a) Write a system of equations representing how much each company charges.

b) If you talk about 20 minutes a day, which plan would be the best deal? (Use 30 days in a month.)

c) After how many minutes would each plan cost the same?

Answer 1

A = 40 + .1(M-500) for M>500

B = 25 + .05M

20 minutes a day for 30 days = 600 minutes per month

A(600) = 40+.1(100) = $50

B(600) = 25 + .05(100) = $30

Plan B is less expensive

40+.1(M-500)= 25+.05M

40-25- .1(500) = .05-.1M

.05M = 35

M= 35/.05 = 700 minutes will have the same cost under plan A or B

40+.1(200) = $60 under plan A

25+.05(700) = $60 under plan B