# Coffee cup finance

Calculus Level 2

To use a coffee machine, you fill a drinking cup with water, pour the water into the reservoir, and then put your cup under the spout. Once the water is heated, it flows through coffee grounds and into your cup. Once you use a cup to drink, it is coated with sugar, coffee, and other residues that would ruin the internal workings of the coffee machine, so you cannot reuse the cup.

If instead, you use two cups, one that you always use to fill the coffee machine with water, and a second that you always use to collect the coffee, you can limit the number of coffee cups you have to use in total to two.

Question: Which of the following functions describes your fractional savings in the total number of coffee cups you've had to use as a function of $c$, the number of cups of coffee you've made?

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