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Q1. Records on a fleet of trucks reveal that the average life of a set of spark plugs is normally distributed with a population mean of 22,100 miles. A manufacturer of spark plugs claims that its plugs have an average life in excess of 22,100 miles. The fleet owner purchased 18 sets and found that the sample average life was 23,400 miles, the sample standard deviation was 1,500 miles and the calculated value of t = 3.677. Based on these findings, is there enough evidence to accept the manufacturer's claim at the 0.05 level. (Explain your answer)
Q2. The mean life of a battery used in a digital clock is 305 days. The lives of the batteries follow the normal distribution. The battery was recently modified to last longer. A sample of 20 of the modified batteries had a mean life of 311 days with a standard deviation of 12 days. You have been asked to test if the modifications have increased the mean life of the batteries at the .05 significance level.
a) State the null & alternative hypothesis:
b) Compute the test statistic and indicate your decision regarding the null hypothesis? Hint: First determine your decision rule.
Q3. As a region sales manager you are interested in testing if there is a difference in sales close rates between two of your sales regions. In the west region you contacted 50 sales people and found that they closed a sale at a rate of 40% of the time. The East region had a higher close rate at 50% based on a sample of 80. In the space below write the formula for the test statistic used to evaluate the difference. Second complete (fill in the values) the formula using the information above. Do not calculate the final value of the test statistic.
Case Problem - Stateline Shipping and Transport Company and Read the "Stateline Shipping and Transport Company" Case Problem.
On average, you receive 2 telemarketing calls per day. What is the probability that you will not receive any telemarketing calls today.
A sample of 121 provided a sample mean of 77.3. The population standard deviation is known to be 16.5. Compute the value of the test statistic.
Would it be reasonable to conclude that the population mean is 63 pounds?
An element E has a constant failure rate λ and a reliability at time t of R(t)=p, if p=0.5 and 0.9, what is the effect on Rs(t), basic reliability, serial Mean Time Between Failure, hs(t), MTBFs if additional elements are added to the baseline sys..
Find a 90 percent confidence interval estimate of the population mean and what is the 95 percent confidence interval estimate of the population mean.
Interpret the results. Is it possible that, for these populations of days, the average number of calls completed between plumber A and plumber B do not differ?
Using the 0.05 level of significance, is there evidence that the population mean is above $300? What is your answer in (a) if s = $90 and the 0.10 level of significance is used?
A company is filling bags of rock salt to a level of 50 pounds. It believes that all bags are filled correctly, but would like to use a hypothesis test with an alpha of 0.05 to check this belief. The company will be using samples of 100 bags from eac..
Do these data provide suffiient evidence to establish that the site is acceptable? Use = 0:05. What are the consequences of Type I and Type II errors? Which error is more expensive to make?
Given the standardized normal distribution (with a mean of 0 and a standard deviation of 1, as in Table E.2), what is the probability that:
Plot the data on U.S. general aviation shipments (b) Describe the patterns and discuss possible causes.(c) Would a fitted trend be helpful? Explain. (d) Make a similar graph for 1992-2003 only.
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