Question 971891
I would use a Poisson distribution: discrete, small, could theoretically be infinite, and no other information here available.
lambda=4

e(-4)=0.01832  That is the probability of 0.
probability of 4= e (-4) 4^4/4! = 0.2930  (expected value)
probability of 4 or fewer is 0.629 from table
probability of 4 or more are waiting is 0.371 (from ≥4 + 0.2930 (4 exactly)=0.664