Question $3$

$10$ pts

Students arrive at a class registration booth at the rate of $4$ per hour. The administrators serve students in a first$-$come, first$-$serve priority with the average service time of $10$ minutes. What is the mean number of students in the system?

$0\mathrm{.}67$

$15$

$2\mathrm{.}0$

$1\mathrm{.}0$

$1\mathrm{.}33$