this is a problem from my Advanced Math class

[chilledsoup]

Amy needs to buy a new gas water heater and has narrowed her choice down to two different models. One model has a purchase price of $278.00 and will cost $17.00 per month to operate. The initial cost of the second model is $413.00 but because of the higher energy factor rating it will cost an average of $11.00 a month to operate.

a. Construct a model to compare the costs of each water heater using equations and graphs.

b. Explain which model would be the better buy.

 

[stapel]

a) What is the (fixed) initial cost of the first model? What is the monthly cost to be added to that? If she uses the thing for one month, what will the cost be? For two months? For three months? Follow the pattern to write an expression for her cost for using it for "x" months. Write a similar expression for the cost of the other model.

b) Make the assumption that she plans to use the machines "forever". Which has the lower long-term cost? (Look at the right-hand side of your graph. Which line is lower?)

Eliz.