A popular retail store knows that the distribution of purchase amounts by its customers is approximately normal with a mean of $30 and a standard deviation of $9. Below you will find normal probability and percentile calculations related to the customer purchase amounts.


Probability Calculations

P(Sales < $ 15.00) = 0.048, P(Sales < $ 20.00) = 0.133,

P(Sales < $ 25.00) = 0.289, P(Sales < $ 35.00) = 0.711


Percentiles Calculations

1st Percentile = $9.06, 5th Percentile = $15.20,

95th Percentile = $44.80, 99th Percentile = $50.94


What two dollar amounts, equidistant from the mean of $30, such that 90% of all customer purchases are between these values?