According to The World Bank, only 9% of the population of Uganda had access to electricity as of 2009. Suppose we randomly sample 150 people in Uganda. Let X = the number of people who have access to electricity.Using the formulas, calculate the mean and standard deviation of X.
In this case, we are given sample size n and probability p so this is a binomial distribution.
We can use the normal approximation where the mean is np and the standard deviation is the square root of npq where q=1-p. Then mean is 150*.09=13.5 and the standard deviation is the square root of 12.285 or 3.5.
I used Excel here but basically, I calculated the binomial probability with n=150, p=.09, and x=15 to be: .099
The cumulative binomial probability with n=150, p=.09, and x=10 is .1987
The cumulative binomial probability of having at most 25 people have electricity (n=150,p=.09, x=25) is 99.9%. So the probability of having more than 25 people is 1-.999=.0001.
Hope that helps!