Quanitive Methods
posted by Tam on .
A car rental company has $540,000 to purchase up to 25 new cars of two different models. One model costs $18,000 each and the other model costs $24,000 each. Write a system of linear inequalities to describe the situation. Let x represent the first model and y represent the second. Find the region described by the system of linear inequalities.

Well, you know that you have 540,000 dollars to spend, so model x*18,000 + y*24,000 < 540,000.
Next, you know that at most, you may buy 25 new cars, so x + y < 25.
If you treat these two inequalities as equations, you can solve for the extreme points. That is say:
x+y = 25 so
y = 25  x. Plug y into the first equation and you get 540,000 = x*18,000 + (25x)*24,000.
Solve for x:
540 = 18x + 600  24x
60 = 6x
x = 10
plug in x=10 into x+y = 25 and you get:
10 + y = 25
y = 15
So, if you buy 10 x model, and 15 y model cars, you'll spend all your money, and have the most cars possible. However, remember that these were inequalities. There is nothing stopping you from spending all your money on model x, or all of it on model y. Also, nothing says that you have to spend all your money either. If you spent all your money on model x, you would get 540,000 / 18,000 = 30 of those. If you spent it all on model y, you would get 22.5 of them. To show the region described by the system, I would make a two sided graph that looks like this:
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_________ The left vertical line is model x, the right is model y. Going across the bottom is increasing model x and decreasing model y. The yintercept on the left axis is 30, and the yintercept on the right axis is 22.5. Where the two cross in the middle is where you get the most car for your money.
Best of luck! 
Sorry, the formatting on the graph got messed up. It should be a horizontal line with two vertical lines sticking up at each end.