Exam 8: Interval Estimation

The manager of a department store wants to determine what proportion of people who enter the store use the store's credit cards for their purchases. What size sample should he take so that at 95% confidence the error will not be more than 6%?

In interval estimation, as the sample size becomes larger, the interval estimate

Exhibit 8-5 A random sample of 64 SAT scores of students applying for merit scholarships showed an average of 1400 with a standard deviation of 240. -Refer to Exhibit 8-5. If we want to provide a 95% confidence interval for the SAT scores, the degrees of freedom for reading the critical values of "t" statistic is

In a sample of 400 registered voters, 204 were Democrats. a.Provide a 95% confidence for the proportion of registered Democrats voters in the population. b.There are 169 million registered voters in the US. Determine an interval for the number (how many) of registered Democrats in the population.

Using an $\alpha$ = 0.04 a confidence interval for a population proportion is determined to be 0.65 to 0.75. If the level of significance is decreased, the interval for the population proportion

Exhibit 8-1 In order to estimate the average time spent on the computer terminals per student at a local university, data were collected for a sample of 81 business students over a one-week period. Assume the population standard deviation is 1.8 hours. -Refer to Exhibit 8-1. The standard error of the mean is

If the population standard deviation of the lifetime of washing machines is estimated to be 900 hours, how large a sample must be taken in order to be 97% confident that the margin of error will not exceed 100 hours?

The manager of a grocery store wants to determine what proportion of people who enter his store are his regular customers. What size sample should he take so that at 97% confidence the margin of error will not be more than 0.1?

Exhibit 8-5 A random sample of 64 SAT scores of students applying for merit scholarships showed an average of 1400 with a standard deviation of 240. -Refer to Exhibit 8-5. The margin of error at 95% confidence is

The following random sample from a population whose values were normally distributed was collected.10 8 11 11 The 95% confidence interval for $\mu$ is

A random sample of 1000 people was taken. Four hundred fifty of the people in the sample favored Candidate A. The 95% confidence interval for the true proportion of people who favors Candidate A is

Exhibit 8-5 A random sample of 64 SAT scores of students applying for merit scholarships showed an average of 1400 with a standard deviation of 240. -Refer to Exhibit 8-5. The "t" value for this interval estimation is

A random sample of 144 observations has a mean of 20, a median of 21, and a mode of 22. The population standard deviation is known to equal 4.8. The 95.44% confidence interval for the population mean is

A small stock brokerage firm wants to determine the average daily sales (in dollars) of stocks to their clients. A sample of the sales for 36 days revealed average daily sales of $200,000. Assume that the standard deviation of the population is known to be $18,000. a.Provide a 95% confidence interval estimate for the average daily sale. b.Provide a 97% confidence interval estimate for the average daily sale.

Exhibit 8-2 A random sample of 121 automobiles traveling on an interstate showed an average speed of 65 mph. From past information, it is known that the standard deviation of the population is 22 mph. -Refer to Exhibit 8-2. If we are interested in determining an interval estimate for $\mu$ at 96.6% confidence, the Z value to use is

In a random sample of 144 observations, = 0.6. The 95% confidence interval for P is

A random sample of 81 credit sales in a department store showed an average sale of $68.00. From past data, it is known that the standard deviation of the population is $27.00. a.Determine the standard error of the mean. b.With a 0.95 probability, what can be said about the size of the margin of error? c.What is the 95% confidence interval of the population mean?

A random sample of 87 airline pilots had an average yearly income of $99,400 with a standard deviation of $12,000. a.If we want to determine a 95% confidence interval for the average yearly income, what is the value of t? b.Develop a 95% confidence interval for the average yearly income of all pilots.

In interval estimation, the t distribution is applicable only when

The average monthly electric bill of a random sample of 256 residents of a city is $90 with a standard deviation of $24. a.Construct a 90% confidence interval for the mean monthly electric bills of all residents. b.Construct a 95% confidence interval for the mean monthly electric bills of all residents.