for the question : Members of the Beta Upsilon Zeta Fraternity each drink a random number of beers with mean 6 and standard deviation 3.

for the question : Members of the Beta Upsilon Zeta Fraternity each drink a random number of beers with mean 6 and standard deviation 3. If there are 81 fraternity members, how much should they buy so that using the normal approximation they are 93.32% sure they will not run out? You just answer me. I want to ask why the standard deviation is 3/(81)^0.5 instead of 3