Question 1

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 2

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 3

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 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

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 6

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?

Accepted Answer

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

Question 7

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.
b.Assume that a sample of 62 students was selected (with the same mean and the standard 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 8

A local university administers a comprehensive examination to the recipients of a B.S. degree in Business Administration. A sample of 5 examinations is selected at random and scored. The scores are shown below.  
a.Compute the sample mean and the standard deviation.
b.Determine the margin of error at 95% confidence.
c.At 95% confidence, determine an interval for the mean of the population.
At 98% confidence, determine an interval for the mean of the population.

Accepted Answer

The answer of A local university administers a comprehensive examination...

Question 9

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 10

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 11

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 12

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 13

Below you are given ages that were obtained by taking a random sample of 9 undergraduate students. Assume the population has a normal distribution.
40
42
43
39
37
39
a.What is the point estimate of $\mu$?
b.Determine the standard deviation.
c.Construct a 90% confidence interval for the average age of undergraduate students.
d.Construct a 99% confidence interval for the average age of undergraduate students.
e.Discuss why the 99% and 90% confidence intervals are different.

Accepted Answer

The answer of Below you are given ages that were...

Question 14

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 15

You are given the following information obtained from a random sample of 6 observations. Assume the population has a normal distribution.  
a.What is the point estimate of $\mu$?
b.Construct an 80% confidence interval for $\mu$.
c.Construct a 98% confidence interval for $\mu$.
d.Discuss why the 80% and 98% confidence intervals are different.

Accepted Answer

The answer of You are given the following information obtained...

Question 16

A university planner is interested in determining the percentage of spring semester students who will attend summer school. She takes a pilot sample of 160 spring semester students discovering that 56 will return to summer school.
a.Construct a 95% confidence interval estimate for the percentage of spring semester students who will return to summer school.
b.Using the results of the pilot study with a 0.95 probability, how large of a sample would have to be taken to provide a margin of error of 3% or less?

Accepted Answer

The answer of A university planner is interested in determining...

Question 17

A new brand of chocolate bar is being market tested. Four hundred of the new chocolate bars were given to consumers to try. The consumers were asked whether they liked or disliked the chocolate bar. You are given their responses below.  
a.What is the point estimate for the proportion of people who liked the chocolate bar?
b.Construct a 95% confidence interval for the true proportion of people who liked the chocolate bar.
c.With a .95 probability, how large of a sample needs to be taken to provide a margin of error of 3% or less?

Accepted Answer

The answer of A new brand of chocolate bar is...

Question 18

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 19

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 20

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...

Quiz 8: Interval Estimation