Help calculating probability

#1
A particular help desk, always has fifteen operators on duty. On average only fourteen operators are simultaneously busy helping customers.

(i) What is the probability that all operators will be simultaneously busy? Briefly explain the approach used.

(ii) What is the probability that one or more callers will have to wait for an operator to become available? Briefly explain the approach used.

I really need help solving this I don't even know where to start. Would greatly appreciate any help.
 
#3
On average only fourteen operators are simultaneously busy helping customers.
Seems to me there's an incomplete representation of the variance in operator availability needed to answer the follow-up questions: The standard deviation. As in for example 14 +/- 1.3 operators busy.