Standard deviation question: Studies show an XBox controller has an average lifetime of 1,500 days. Assume the lifetimes are normally distributed with a standard deviation of 325 days.
A: Find the percentage of controllers that will fail during their first 895 days of use.
B: Find the percentage of controllers that will fail within 225 days of their average lifetime. (NOT the first 225 days!)
C: At what number of days should the lifetime warranty be set so that fewer than 3.5% of the controllers must be replaced under warranty?