A real estate agent is considering changing her cell phone plan; there are three to chose from - all involve a monthly fee of $19.25 Plan A charges $0.37 per minute for daytime calls and $0.18 per minute for evening calls. Plan B charges $0.58 per minute for daytime calls and $0.18 per minute for evening calls. Plan C has a flat rate of $33 with up to 200 minutes of calls included per month and a charge of $0.31 per minute beyond that, day or evening. a. Determine the total charge under each plan for this case: 120 minutes of day calls and 40 minutes of evening calls in a month.
b. If the agent will use the service for daytime calls only, how many minutes per month should she stay below so that Plan A is the least cost alternative?
c. Suppose that the agent expects both daytime and evening calls. At what point (i. e., percentage of total call minutes used for daytime calls) would she be indifferent between plans A and B?