A manufacturer wishes to estimate the reliability (in months) of a certain product. An estimate of the population standard deviation from a previous sample was 12 months. If the manufacturer desires to be within 4 months of the true value with approximately 80% confidence, what should the sample size be?

The overall average on a process you are attempting to monitor is 50.0 units. The process population standard deviation is 1.84. Sample size is given to be 16.

A survey of 30 adults found that the mean age of a person's vehicle is 3.6 years. Assuming the population distribution is normal and the standard deviation is 2 years, find the 94% confidence interval for the population mean. What is the meaning of this confidence interval?

There are many situations in which we want to compare means from populations having standard deviations that are equal. This method applies even if the standard deviations are known to be only approximately equal. Consider a report regarding average incidence of fox rabies in two regions. For region I, n1 = 16, x1 ≈ 4.73, and s1 = 2.84 and for region II, n2 = 15, x2 ≈ 3.93, and s2 = 2.45. The two sample standard deviations are sufficiently close that we can assume ?1 = ?2. Use the method of pooled standard deviation to consider the report, testing if there is a difference in population mean average incidence of rabies at the 5% level of significance. (Round your answer to three decimal places.) t =

Suppose we wish to calculate a 90% confidence interval for the average amount spent on books by freshmen in their first year at a major university. The interval is to have a margin of error of $2. Assume that the amount spent on books by freshmen has a normal distribution with a standard deviation of $30. How many observations are required to achieve this margin of error?

A recent survey of 25 students showed that they spent an average of $18.53 on petrol eachweek. The standard deviation of the sample was $3.00. Find the 99% confidence intervalfor the true mean (average over all students).

Executives at a car dealership want to estimate the average age of their customers before making a television commercial. They want to be 90% confident that the mean age is ±2 years of the sample mean. If the standard deviation from a previous study is 12 years, how large should the sample be? 98 ODD 239 4 139