Could someone clarify this question?
Assume that inter-arrival times of student arriving at the canteen are exponentially distributed with a mean of $\dfrac13$.
a) Find the probability that no students arrive during a $20$ minutes interval.
b) Find the probability that more than two students arrive during the server's ten-minute break.
For part (a), how would I find the the probability of $x=0$ students when exponential distribution only works for $x$ less or equal to a number? Do I need to use Poisson?
For part (b) how would I go about using the break time? It doesn't make sense to me.