statistics
posted by larae on .
The personnel office at a large electronics firm regularly schedules job interviews and maintains records of the interviews. From the past records, they have found that the length of a first interview is normally distributed, with mean μ = 31 minutes and standard deviation σ = 7 minutes.
(a) What is the probability that a first interview will last 40 minutes or longer? (Use 3 decimal places.)
(b) Two first interviews are usually scheduled per day. What is the probability that the average length of time for the two interviews will be 40 minutes or longer? (Use 3 decimal places.)

Z = (scoremean)/SD
Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability related to the Z score.
If the events are independent, the probability of both/all events occurring is determined by multiplying the probabilities of the individual events.