A videotape store has an average weekly gross of $\$1,158$ with a standard deviation of $\$120$. The store's gross receipts during a randomly selected week follow a normal distribution.
a.) What is the probability of grossing less than $1,000 in a week?
b.) What is the 80th percentile of weekly gross receipts?
(a) The probability is
(b) We need to find C such that