SOLUTION: 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.

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Question 976639: 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 between $20 and $35 at this store?
Answer by FrankM(1040) About Me  (Show Source):
You can put this solution on YOUR website!
One SD is $9, and you are asking about +/- $5 which is .55 sds.
A z score of .55 results in 20.9% but with +/- we need to double this to 41.8%.