Public Health and Nutrition The Food and Drug Administration (FDA) reviews all advertisements for drugs to check for omissions regarding a drug's risk; inadequate, incorrect, or inconsistent labeling; misleading claims; unsupported comparative claims; and unapproved purposes. Lengthy legal reviews of advertisements have increased the total review time. Suppose the length of time between a request for a review and final approval has a normal distribution with mean μ = 21 days and σ = 4 days. Consider a randomly selected advertisement submitted to the FDA for review.
a. What is the probability that the advertisement will be reviewed in less than 14 days?
b. What is the probability that the advertisement will be reviewed in between 15 and 19 days?
c. Suppose the advertisement takes at least 20 days for review. What is the probability that it will take less than 30 days for review?
d. Suppose two independent advertisements are submitted for review simultaneously. What is the probability that both will take more than 30 days for review?