sampling distribution

An automobile parts supplier wants to know how long car owners plan to keep their cars with them. A random sample of 20 car owners results in a standard deviation of 3.7 years. Find a 95% confidence interval for the variance and standard deviation. Assume that the variable is normally ..

A manufacturer of bulbs claims that the variance of the span of life of the bulbs is 320 hours. The inspection department selected a random sample of 15 bulbs and found the variance as 210 hours. Find the chi-square test value. At α = 0.05, is there enough evidence to reject the man..

A city University believes that 50% of the incoming students would take economics, 25% would take arts, and 25% would take engineering. A sample of the student population shows the following distribution. Course Economics Arts Engineering Number of students 38 23 19 At α =..

The standard deviation of the annual income of a random sample of 20 doctors in U.S. having one to two years experience is $5900. Test the hypothesis that the standard deviation of the population is more than $5,400 a year at α = 0.05. Also write the chi-square test value. [Assume t..

In a report, the standard deviation of the weights of male student athletes is stated as 2 pounds. The standard deviation of weight of a random sample of 24 male student athletes was found as 1.9 pounds. Find the chi-square test value. At α = 0.01 is there enough evidence to support..

Select the incorrect statement(s). I. If a confidence interval does not include H 0 , then a hypothesis test will reject H 0 . II. If a confidence interval include H 0 , then a hypothesis test will reject H 0 III.For testing H 0 , t distribution is appropriate when the standard deviation ..

A company claims that the standard deviation of the gear speed for a piece of machinery is 28 revolutions per minute (rpm). An engineer selected a random sample of 20 machines and found the standard deviation as 40 (rpm). At α = 0.01, is there enough evidence to reject the company's..

The frequency distribution represents the data obtained from a sample of computer repairs. The values are the mean time (in hours) between repairs on 80 machines. Mean time between repairs Number of machines 25.5 - 28.5 5 28.5 - 31.5 9 31.5 - 34.5 32 34.5 - 37.5 20 37.5 - 40.5 1..

A random sample of the assets (in millions of dollars) of 10 families of a colony is shown. Find the 80% confidence interval for the variance of the assets. Assume that the variable is normally distributed. 0.5 1 0.4 1.3 0.8 1.2 0.9 2 0.7 1.5 => between 0.158 and 0.529 or betwee..

The sales in dollars of a new store for a random sample of 10 days in a month are as follows. 450 600 540 650 480 520 680 590 610 550 At α = 0.01, is there enough evidence for the merchandiser to conclude that the standard deviation of the sales per day is more than $60? What is the..