Question

A group of friends rent a house at the beach for spring break. If nine of them share the house, it costs $150 each. Is the cost to each person directly or inversely proportional to the number of people sharing the house?

Answer 1

Inversely: as the number of people increases the individual cost decreases.

Explanation:

I think that the idea of sharing is exactly this: if the number of people (sharing) increases the cost for each one decreases.
Considering, for example, your data you have 9 people sharing and paying `$150` each, it gives a total of `9xx$150=$1350`.
Adding one person (number increases) you'll get `(1350$)/10=$135` representing a decrease from `$150`.
Your cost `C` can be modelled by a function such as:
`C(x)=(1350$)/x` where `x` is the number of persons.