Suppose that ice cream consumption per person at parties is normally distributed with a mean of 0.39 gallons, and a standard deviation of 0.26 gallons. If you are throwing a party with 33 guests, how much ice cream do you need to buy to make sure that the probability of having enough is 95%?

Question

I am not sure how to work this problem. do I change the 95 % to .95 the subtract .39 and then .26/sqrt33. This is how I started and it is not correct the teacher said answer was 16 gals

Answer 1

from the Z table, 95% are below 1.645 std above the mean

That means .39 + 1.645*.26 = .8177

So, there's a 95% chance that the average consumption is below .8177 gallons

For 33 people , that means that there's a 95% chance that .8177*33 = 26.98 gallons will fed them all.

Answer 2

Not sure how the answer is 16 gallons. Better check my math.