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Confidence Interval and Sample Size for Carry on Luggage

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Mean weight of carry-on luggage
Mean of a population
Lifetimes of washing machines
Proportion of Democrats in sample of registered voters
Proportion of customers who use stor credit card for purchases

In order to determine the average weight of carry-on luggage by passengers in airplanes, a sample of 36 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.
You are given the following information obtained from a random sample of 4 observations taken from a large, normally distributed population.
25 47 32 56
Construct a 95% confidence interval for the mean of the population.

If the standard deviation for the lifetimes of washing machines is estimated to be 800 hours, how large a sample must be taken in order to be 97% confident that the margin of error will not exceed 50 hours?

In a random sample of 200 registered voters, 120 indicated they are Democrats. Develop a 95% confidence interval for the proportion of registered voters in the population who are Democrats.

The manager of a department store wants to determine what proportion of people who enter the store use the store's credit card for their purchases. What size sample should he take so that at 99% confidence the error will not be more than 8%?

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Solution Summary

The solution provides step by step method for the calculation of confidence interval for mean and sample size. Formula for the calculation and Interpretations of the results are also included. The user can edit the inputs and obtain the complete results for a new set of data.

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Proportion

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16. A study of 305 computer chips found that 244 chips functioned properly. Develop a 99 percent confidence interval for the population proportion of properly functioning computer chips.
17. A correctional institution would like to report the mean amount of money spent per day on operating the facilities. How many days should be considered if a 95 percent confidence is used and the estimate is to be within one hundred dollars? The standard deviation is $400.

18. The Corporate Lawyer, a magazine for corporate lawyers, would like to report the mean amount earned by lawyers in their area of specialization. How large a sample is required if the 97 percent level of confidence is used and the estimate is to be within $2,500? The standard deviation is $16,000.

19. The Customer Relations Department at Commuter Airline, Inc. wants to estimate the proportion of customers that carry only hand luggage. The estimate is to be within 0.03 of the true proportion with 95 percent level of confidence. No estimate of the population proportion is available. How large a sample is required?

20. A survey is being conducted on a local mayoral election. If the poll is to have a 98 percent confidence interval and must be within four percentage points, how many people should be surveyed?

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