Question 1

The monthly starting salaries of students who receive an MBA degree have a population standard deviation of
$110. What size sample should be selected to obtain a 0.95 probability of estimating the mean monthly income within $20 or less?

Accepted Answer

The answer of The monthly starting salaries of students who...

Question 2

A random sample of 100 credit sales in a department store showed an average sale of $120.00. From past data, it is known that the standard deviation of the population is $40.00.
a. Determine the standard error of the mean.
b. With a 0.95 probability, determine the margin of error.
c. What is the 95% confidence interval of the population mean?

Accepted Answer

The answer of A random sample of 100 credit sales...

Question 3

The proprietor of a boutique in New York wanted to determine the average age of his customers. A random sample of 53 customers revealed an average age of 28 years with a standard deviation of 4 years. Determine a 98% confidence interval estimate for the average age of all his customers.

Accepted Answer

The answer of The proprietor of a boutique in New...

Question 4

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%?

Accepted Answer

The answer of The manager of a department store wants...

Question 5

A sample of 36 patients in a doctor's office showed that they had to wait an average of 45 minutes with a standard deviation of 10 minutes before they could see the doctor. Provide a 90% confidence interval estimate for the average waiting time of all the patients who visit this doctor.

Accepted Answer

The answer of A sample of 36 patients in a...

Question 6

The Highway Safety Department wants to study the driving habits of individuals. A sample of 121 cars traveling on the highway revealed an average speed of 60 miles per hour with a standard deviation of 11 miles per hour. Determine a 95% confidence interval estimate for the speed of all cars.

Accepted Answer

The answer of The Highway Safety Department wants to study...

Question 7

A coal company wants to determine a 95% confidence interval estimate for the average daily tonnage of coal that they mine. Assuming that the company reports that the standard deviation of daily output is 200 tons, how many days should they sample so that the margin of error will be 39.2 tons or less?

Accepted Answer

The answer of A coal company wants to determine a...

Question 8

In a poll of 600 voters in a campaign to eliminate non-returnable beverage containers, 210 of the voters were opposed. Develop a 92% confidence interval estimate for the proportion of all the voters who opposed the container control bill.

Accepted Answer

The answer of In a poll of 600 voters in...

Question 9

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?

Accepted Answer

The answer of The manager of a grocery store wants...

Question 10

If the standard deviation of the lifetime of a vacuum cleaner is estimated to be 300 hours, how large of a sample must be taken in order to be 97% confident that the margin of error will not exceed 40 hours?

Accepted Answer

The answer of If the standard deviation of the lifetime...

Question 11

A local health center noted that in a sample of 400 patients 80 were referred to them by the local hospital.
a. Provide a 95% confidence interval for all the patients who are referred to the health center by the hospital.
b. What size sample would be required to estimate the proportion of hospital referrals with a margin of error of 0.04 or less at 95% confidence?

Accepted Answer

The answer of A local health center noted that in...

Question 12

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.

Accepted Answer

The answer of A small stock brokerage firm wants to...

Question 13

In order to estimate the average electric usage per month, a sample of 196 houses was selected, and their electric usage determined.
a. Assume a population standard deviation of 350-kilowatt hours. Determine the standard error of the mean.
b. With a 0.95 probability, determine the margin of error.
c. If the sample mean is 2,000 KWH, what is the 95% confidence interval estimate of the population mean?

Accepted Answer

The answer of In order to estimate the average electric...

Question 14

Computer Services, Inc. wants to determine a confidence interval for the average CPU time of their teleprocessing transactions. A sample of 64 transactions yielded a mean of 6 seconds with a standard deviation of 0.8 seconds. Determine a 98% confidence interval for the average CPU time.

Accepted Answer

The answer of Computer Services, Inc. wants to determine a...

Question 15

In order to determine how many hours per week freshmen college students watch television, a random sample of 256 students was selected. It was determined that the students in the sample spent an average of 14 hours with a standard deviation of 3.2 hours watching TV per week.
a. Provide a 95% confidence interval estimate for the average number of hours that all college freshmen spend watching TV per week.
Assume that a sample of 62 students was selected with the same mean and the standard
b. deviation). Provide a 95% confidence interval estimate for the average number of hours that all college freshmen spend watching TV per week.

Accepted Answer

The answer of In order to determine how many hours...

Question 16

In order to determine the average weight of carry-on luggage by passengers in airplanes, a sample of 16 pieces of carry-on luggage was weighed. The average weight was 20 pounds. Assume that we know the standard deviation of the population to be 8 pounds.
a. Determine a 97% confidence interval estimate for the mean weight of the carry-on luggage.
b. Determine a 95% confidence interval estimate for the mean weight of the carry-on luggage.

Accepted Answer

The answer of In order to determine the average weight...

Question 17

A random sample of 81 children with working mothers showed that they were absent from school an average of 6 days per term with a standard deviation of 1.8 days. Provide a 95% confidence interval for the average number of days absent per term for all the children.

Accepted Answer

The answer of A random sample of 81 children with...

Question 18

In a random sample of 400 residents of Chattanooga, 320 residents indicated that they voted for the Democratic candidate in the last presidential election. Develop a 95% confidence interval estimate for the proportion of all Chattanooga residents who voted for the Democratic candidate.

Accepted Answer

The answer of In a random sample of 400 residents...

Question 19

The average score of a sample of 87 senior business majors at UTC who took the Graduate Management Admission Test was 510 with a standard deviation of 36. Provide a 98% confidence interval for the mean of the population.

Accepted Answer

The answer of The average score of a sample of...

Question 20

A statistician employed by a consumer testing organization reports that at 95% confidence he has determined that the true average content of the Uncola soft drinks is between 11.7 to 12.3 ounces. He further reports that his sample revealed an average content of 12 ounces, but he forgot to report the size of the sample he had selected. Assuming the standard deviation of the population is 1.28, determine the size of the sample.

Accepted Answer

The answer of A statistician employed by a consumer testing...

Quiz 8: Interval Estimation

The monthly starting salaries of students who receive an MBA degree have a population standard deviation of $110. What size sample should be selected to obtain a 0.95 probability of estimating the mean monthly income within $20 or less?