1.A library determines that its books are returned on time 90% of the time. If 450 books are checked out, what is the probability that more than 400 will be returned on time?
2. Suppose that replacement times for washing machines are normally distributed with a mean of 9.3 years and a standard deviation of 1.1 years. Find the probability that 70 randomly selected washing machines will have a mean replacement time of less than 9.1 years.
3. For the binomial distribution with the given values for n and p, state whether or not it is suitable to use the normal distribution as an approximation. n = 18 and p = .2
4. Suppose that replacement times for washing machines are normally distributed with a mean of 9.3 years and a standard deviation of 1.1 years. Find the probability that 70 randomly selected washing machines will have a mean replacement time less than 9.1 years.
5. A car rental has cars with an average of 9000 miles and standard deviation of 1200. If 25 cars are in a lot, what is the probability the average miles will be more than 9500 miles?
6.A multiple choice test consists of 60 questions. Each question has 4 possible answers of which one is correct. If all answers are random guesses, estimate the probability of getting at least 20% correct.
7.Assume that women's heights are normally distributed with a mean of 63.6 inches and a standard deviation of 2.5 inches. If 90 women are randomly selected, find the probability that they have a mean height between 62.9 inches and 64.0 inches.
8. Two percent of CD-ROM drives produced in a certain plant are defective. Estimate the probability that of 10,000 randomly selected drives, at least 219 are defective.