Question

A milk company unconditionally guarantees that an unopened, properly refrigerated container of its milk will be fresh for 5 days after the date stamped on the carton. The company's data shows that unopened containers remain fresh on average for 6 days, with a standard deviation of 0.65 days. Assume that the length of time milk stays fresh follows a normal distribution. What percent of the milk containers will spoil in greater than 7 days after the date stamped?

Answer 1

(7-6)/0.65 = 1.538 std
so, look that up in your Z table to see how much lies in the right tail.