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As the number of degrees of freedom for a t distribution increases, the difference between the t distribution and the standard normal distribution
What assumption must be made before we can determine an interval for the mean grade of all the students in the class? Explain why.
Based on the above information, determine the confidence coefficient that was used. Assume the population has a normal distribution.
Many people who bought X-Game gaming systems over the holidays have complained that the systems they purchased were defective. In a sample of 1200 units sold, 18 units were defective. Determine a 9
Choo Choo Paper Company produces papers of various thickness. A random sample of 256 cuts had a mean thickness of 30.3 mils with a standard deviation of 4 mils. Develop a 95% confidence interval for
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. Determine the standard
You are given the following information obtained from a sample of 5 observations taken from a population that has a normal distribution. Develop a 98% confidence interval estimate for the mean of the
Is it necessary to know anything about the shape of the distribution of the account balances in order to make an interval estimate of the mean of all the account balances? Explain.
With a .95 probability, what statement can be made about the size of the margin of error?
A sample of 60 students from a large university is taken. The average age in the sample was 22 years with a standard deviation of 6 years. Construct a 95% confidence interval for the average age of
Construct a 95% confidence interval for the mean of the population, assuming the population has a normal distribution.
A researcher is interested in determining the average number of years employees of a company stay with the company. If past information shows a standard deviation of 7 months, what size sample shoul
Below you are given ages that were obtained by taking a random sample of 9 undergraduate students. Assume the population has a normal distribution.Determine the standard deviation.
The makers of a soft drink want to identify the average age of its consumers. A sample of 55 consumers was taken. The average age in the sample was 21 years with a standard deviation of 4 years. Co
It is known that the variance of a population equals 1296. A random sample of 144 observations is going to be taken from the population.
a. Compute the standard error of the mean (in dollars). b. Compute the margin of error (in dollars) at 95% confidence.
A random sample of 81 students at a local university showed that they work an average of 60 hours per month with a standard deviation of 18 hours. Compute a 95% confidence interval for the mean of t
After computing a confidence interval, the user believes the results are meaningless because the width of the interval is too large. Which one of the following is the best recommendation?
Using an a = 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
A machine that produces a major part for an airplane engine is monitored closely. In the past, 10% of the parts produced would be defective. With a .95 probability, the sample size that needs to be
We are interested in conducting a study in order to determine what percentage of voters of a state would vote for the incumbent governor. What is the minimum size sample needed to estimate the popul
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 mea
A random sample of 64 students at a university showed an average age of 25 years and a sample standard deviation of 2 years. The 98% confidence interval for the true average age of all students in t
A random sample of 49 statistics examinations was taken. The average score, in the sample, was 84 with a variance of 12.25. The 95% confidence interval for the average examination score of the popul
Assuming a population standard deviation of 6 hours, what is the required sample size if the error should be less than 1/2 hour with a 95% level of confidence?