Exam 8: Estimation and Confidence Intervals

A sample of 500 executives who own their own home revealed 175 planned to sell their homes and retire to Victoria. Develop a 98% confidence interval for the proportion of executives that plan to sell and move to Victoria.

A consumer group would like to estimate the mean monthly electricity charge for a single family house in July (within $5) using a 99 percent level of confidence. Based on similar studies the standard deviation is estimated to be $20.00. How large a sample is required?

College X is concerned about their employees making use of their email for non-business purposes. A random sample of 400 e-mails discovered 80 messages that were not business related. The 99% confidence interval for the population proportion is:

College X is concerned about their employees making use of their email for non-business purposes. A random sample of 400 e-mails discovered 70 messages that were not business related. The 95% confidence interval for the population proportion is:

A sample of union members was selected and their opinions regarding the proposed management union contract were recorded with 1,600 out of the 2,000 members in favour of it. Using a 95% confidence level, the interval estimate for the population proportion was computed to be 0.78 and 0.82.

The following summarizes the amount of snowfall in Ontario over the past number of years. Determine a 95% confidence interval for the average annual snowfall.

The proportion of junior executives leaving large manufacturing companies within three years is to be estimated within 3 percent. The 0.95 degree of confidence is to be used. A study conducted several years ago revealed that the percent of junior executives leaving within three years was 21. To update this study, the files of how many junior executives should be studied?

College X is concerned about their employees making use of their email for non-business purposes. A random sample of 400 e-mails discovered 80 messages that were not business related. The 90% confidence interval for the population proportion is:

The z-value associated with a 90% level of confidence is:

A survey of an urban university (population of 25,450) showed that 870 of 1,100 students sampled supported a fee increase to fund improvements to the student recreation center. Using the 99% level of confidence, what is the confidence interval?

The z-value associated with an 80% level of confidence is:

(i. The interval estimate states the range within which a population parameter probably lies. (ii) A 95 percent confidence interval implies that about 95 out of 100 similarly constructed intervals will include the parameter being estimated. (iii) For a sampling distribution of the means, 95% percent of the means would be between $\pm$ 1.96 standard deviations.

(i. The interval estimate states the range within which a population parameter probably lies. (ii). The measure of confidence that one has in the interval estimate is called degree of level of confidence. (iii) For a sampling distribution of the means, 95% percent of the means would be between $\pm$ 1.96 standard deviations.

The Sugar Producers Association wants to estimate the mean yearly sugar consumption. A sample of 16 people reveals the mean yearly consumption to be 27 kg with a sample standard deviation of 9 kg. Assume a normal population. Develop a 90% confidence interval for the mean annual consumption of sugar.