A popular retail store knows that the purchase amounts by it

A popular retail store knows that the purchase amounts by its customers is a random variable that follows a normal distribution with a mean of $30 and a standard deviation of $9.

What is the probability that a randomly selected customer will spend $30 or more at this store?

Solution

So the probability is

P(X>30) = P((X-mean)/s >(30-30)/9)

=P(Z>0)

=0.5 (from standard normal table)