Question 1

An analysis of 97 Wall Street traders showed that 7 of their stock picks beat the market average. What is the estimate of the population proportion? What is the standard error of this estimate?

Question 2

A sample proportion is calculated from a sample size of 470. How large of a sample would we need in order to decrease the standard error by a factor of 10?

Question 3

A sample proportion is calculated from a sample size of 181. How large of a sample would we need in order to decrease the standard error by a factor of 7?

Question 4

Suppose 46.21% of small businesses experience cash flow problems in their first 5 years. A consultant takes a random sample of 572 businesses that have been opened for 5 years or less. What is the probability that less than 46.76% of the businesses have experienced cash flow problems?

Question 5

Suppose the nationwide high school dropout rate for 2010 was around 13.07%. If you take a sample of 488 students in high school in 2010, what is the probability that between 10.03% and 14.05% of them ended up dropping out?

Question 6

The company you work for produces automotive parts for GM. A certain machine that makes a cutout in a piece of steel averages a cut size of 189.2136 mm with a standard deviation of 0.23428 mm. A random sample of 65 is taken from the population. What is the distribution of the sample mean?

Question 7

Suppose that in the United States the typical adult male is 66.37 inches tall with a standard deviation of 4.168. You take a random sample of 34 adult males. What is the probability that the mean height of the sample is between 65.96 and 66.37?

Question 8

Suppose you are interested in measuring the amount of time, on average, it takes you to make your commute to school. You've estimated that the average time is 38.7 minutes with a standard deviation of 6.083 minutes. Over 11 random days, you measure your commute time. Assuming that your estimated parameters are correct, what is the probability that the average commute time over that 11 day period is between 38.2 and 39.52 minutes?

Question 9

You are working as a quality control manager for FedEx and are responsible for delivery time customer satisfaction. Historically, the worldwide average delivery time is 18.61 days with a standard deviation of 3.05 days. You select 74 random deliveries over the course of a few months. Given your historical parameters still hold true, what is the probability that the average time until delivery is between 18.61 and 18.62 days?

Question 10

Suppose that the average score on the STAT 2160 Final Exam is 73.028% with a standard deviation of 6.4447%. For a sample of 14 sections, 65% of sections will have an average greater than what score?

Question 11

Fill in the blank. Suppose that NBA players average 27.27 points per game with a standard deviation of 6.444. A random sample of 48 players is taken. There is a 13% chance that the average points per gameisless than ________ points.