36 drinks total 72 oz with a standard deviation of (1/2)*sqrt(36)=3 oz

The total is normally distributed with mean 72 and sd 3 oz, so the

z-score corresponding to an empty bottle is:

z=(72-63)/3=3

So the probability that the bottle is not empty is:

p(not empty)=1 - P(3)

where P is the cumulative standard normal distribution.

RonL