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.

Answer 1

A's monthly cost = C = 40 + .10(m-500) for over 500 minutes,

C = 40 for 500 or less minutes

a stepwise function

B' monthly cost = C = 25 + .05m

which is best? less expensive?

for 0 </= m < 30 B is cheaper

for m=30 they cost the same

for 30<m < etc.

for very large m B is better