Exam 8: Sampling Methods and the Central Limit Theorem

The wildlife department has been feeding a special food to rainbow trout fingerlings in a pond.A sample of the weights of 40 trout revealed that the mean weight is 402.7 grams and the standard deviation 8.8 grams.What is the probability that the mean weight for a sample of 40 trout exceeds 405.5 grams?

Manufacturers were subdivided into groups by volume of sales.Those with more than $100 million in sales were classified as Class A large;those from $50 to $100 million as Class A medium size;and those between $25 and $50 million... ,and so on.Samples were then selected from each of these groups.What is this type of sampling called?

The standard error of the mean is also called sampling error.

Truck tire life is normally distributed with a mean of 60,000 miles and a standard deviation of 4,000 miles.What is the probability that a tire lasts between 54,000 and 66,000 miles?

Sampling error is the difference between a corresponding sample statistic and the

Which of the following is the standard error of the mean?

Based on the central limit theorem,for a given population,the mean of all the sample means ( )of sample size n,and the mean of all (N)population observations (x)are

What is the relationship of the standard deviation of the sampling distribution of the mean to the standard deviation of the population under study? ___________

Sampling from a population may be preferred because,contacting or listing the entire population would be too ___________ consuming.

The standard error of the mean will vary according to the size of the sample.As the sample size n gets larger,the variability of the sample means gets smaller.

A group of statistics students decided to conduct a survey at their university to find the average (mean)amount of time students spend studying per week.Based on a simple random sample,they surveyed 144 students.The statistics showed that students studied an average of 20 hours per week with a standard deviation of 10 hours.What is the probability of finding a sample mean less than 18 hours?

For populations scattered in a wide area,what is the preferred technique for sampling? ____________

Suppose a research firm conducted a survey to determine the average amount of money steady smokers spend on cigarettes during a week.A sample of 100 steady smokers revealed that the sample mean is $20 and the sample standard deviation is $5.What is the probability that a sample of 100 steady smokers spend between $19 and $21?

It is often not feasible to study the entire population because it is impossible to observe all the items in the population.

A marketing firm is studying consumer preferences for winter fashions in four different months.From a population of women,18-21 years of age,a random sample of 100 women was selected in January.Another random sample of 100 women was selected in March.Another random sample of 100 women was selected in June.Another random sample of 100 women was selected in September.

To determine the value of the standard error of the mean,the total error is divided by the sample size.

A simple random sample assumes that each item or person in the population has an equal chance of being included.

When using stratified random sampling,the sampling error will be zero.

An accounting firm is planning for the next tax preparation season.From last year's returns,the firm collects a systematic random sample of 100 filings.The 100 filings showed an average preparation time of 90 minutes with a standard deviation of 140 minutes.What assumptions do you need to make about the shape of the population distribution of all possible tax preparation times to make inferences about the average time to complete a tax form?

An accounting firm is planning for the next tax preparation season.From last year's returns,the firm collects a systematic random sample of 100 filings.The 100 filings showed an average preparation time of 90 minutes with a standard deviation of 140 minutes.What is the probability that the mean completion time will be more than 120 minutes?