Answer
As $p$ increases, we would expect $N$ to decrease.
Therefore, we would expect $\frac{dN}{dp}$ to be negative.
Work Step by Step
$N$ is the number of people who travel by car to another state for a vacation this year when the average price of gasoline is $p$ dollars per gallon.
If the average price of gasoline is low, we would expect that more people would travel by car on vacation.
If the average price of gasoline is high, we would expect that fewer people would travel by car on vacation.
As $p$ increases, we would expect $N$ to decrease.
Therefore, we would expect $\frac{dN}{dp}$ to be negative.
