Exam 7: Sampling and Sampling Distributions

Which of the following yields a stratified sample?

Major league baseball salaries averaged $3.26 million with a standard deviation of $1.2 million in a recent year. Suppose a sample of 100 major league players was taken. Find the approximate probability that the mean salary of the 100 players was less than $2.5 million.

Which of the following yields a cluster sample?

Selection bias occurs more frequently in systematic samples than in simple random samples.

TABLE 7-7 Online customer service is a key element to successful online retailing. According to a marketing survey, 37.5% of online customers take advantage of the online customer service. Random samples of 200 customers are selected. -Referring to Table 7-7, 95% of the samples proportions symmetrically around the population proportion will have between ________% and ________% of the customers who take advantage of online customer service.

TABLE 7-2 The time spent studying by students in the week before final exams follows a normal distribution with a standard deviation of 8 hours. A random sample of 4 students was taken in order to estimate the mean study time for the population of all students. -Referring to Table 7-2, what is the probability that the sample mean exceeds the population mean by more than 2 hours?

TABLE 7-6 According to an article, 19% of the entire population in a developing country have high-speed access to the Internet. Random samples of size 200 are selected from the country's population. -Referring to Table 7-6, the population mean of all the sample proportions is ________.

Which of the following is true regarding the sampling distribution of the mean for a large sample size?

An electronic appliance chain gathered customer opinions on their services using the customer feedback forms that are attached to the product registration forms. This is an example of a convenience sample.

If you randomly select a student from the first row of a business statistics class and then every other fifth student thereafter until you get a sample of 20 students, this is an example of a convenience sample.

TABLE 7-5 According to a survey, only 15% of customers who visited the web site of a major retail store made a purchase. Random samples of size 50 are selected. -Referring to Table 7-5, the standard deviation of all the sample proportions of customers who will make a purchase after visiting the web site is ________.

The amount of bleach a machine pours into bottles has a mean of 36 oz. with a standard deviation of 0.15 oz. Suppose we take a random sample of 36 bottles filled by this machine. The sampling distribution of the sample mean has a standard error of 0.15.

TABLE 7-5 According to a survey, only 15% of customers who visited the web site of a major retail store made a purchase. Random samples of size 50 are selected. -Referring to Table 7-5, what proportion of the samples will have less than 15% of customers who will make a purchase after visiting the web site?

If the amount of gasoline purchased per car at a large service station has a population mean of 15 gallons and a population standard deviation of 4 gallons, then 99.73% of all cars will purchase between 3 and 27 gallons.

To gather opinions on the efficacy of U.S. foreign policies, a sample of 50 faculty members is selected from the pool of university professors who have taught political science at the graduate level. This is an example of a judgment sample.

The standard deviation of the sampling distribution of a sample proportion is , where π is the population proportion.

TABLE 7-4 The lifetimes of a certain brand of light bulbs are known to be normally distributed with a mean of 1,600 hours and a standard deviation of 400 hours. A random sample of 64 of these light bulbs is taken. -Referring to Table 7-4, what is the probability that the sample mean lifetime is more than 1,550 hours?

Which of the following types of samples can you use if you want to make valid statistical inferences from a sample to a population?

A study at a college on the west coast reveals that, historically, 45% of the students are minority students. If a random sample of size 75 is selected, the probability is ________ that more than half of the students in the sample will be minority students.

TABLE 7-6 According to an article, 19% of the entire population in a developing country have high-speed access to the Internet. Random samples of size 200 are selected from the country's population. -Referring to Table 7-6, among all the random samples of size 200, 90% will have more than ________% who have high-speed access to the Internet.