1. Side effects. Researchers testing a new medication find that 7% of users have side effects. To how many pa- tients would a doctor expect to prescribe the medication before finding the first one who has side effects?
2. Credit cards. College students are a major target for ad- vertisements for credit cards. At a university, 65% of students surveyed said they had opened a new credit card account within the past year. If that percentage is accurate, how many students would you expect to survey before finding one who had not opened a new account in the past year?
3. Missing pixels. A company that manufactures large LCD screens knows that not all pixels on their screen light, even if they spend great care when making them. In a sheet 6 ft by 10 ft (72 in. by 120 in.) that will be cut into smaller screens, they find an average of 4.7 blank pixels. They be- lieve that the occurrences of blank pixels are independent. Their warranty policy states that they will replace any screen sold that shows more than 2 blank pixels.
a) What is the mean number of blank pixels per square foot?
b) What is the standard deviation of blank pixels per square foot?
c) What is the probability that a 2 ft by 3 ft screen will have at least one defect?
d) What is the probability that a 2 ft by 3 ft screen will be replaced because it has too many defects?