Suppose that a rent a car company has 700 cars and the average per rental is 9 days, then we muliply $2.3$ by $700$ in order to find the expected number of bookings per month.
So the expected number of bookings is equal to $700 \cdot \frac{700}{9 \cdot 30} $, right ?
Why does this happen? Could you explain to me the formula?
Well, assuming that as soon as one car is returned, the next car is taken, then an approximation of the number of times each car is used per month is $\displaystyle \frac{30}{9}\approx 3.3$.
Multiply $3.3$ times per car, by $700$ cars, to get around $2333$ rentals per month.