38 Based on a random sample of 13 tire changes the mean time

38. Based on a random sample of 13 tire changes, the mean time to change a tire on a Boeing 777 has a mean of 59.5 minutes with a standard deviation of 8.4 minutes. For 10 tire changes on a Boeing 787 the mean time was 64.3 minutes with a standard deviation of 12.4 minutes. To test for equal variances in a two-tailed test at ? = .10, the critical values are:

3.07 and 0.357

40) Litter sizes (number of pups) for randomly chosen dogs from two breeds were compared. The sample data were entered into Excel, and the following results were produced.

Between .05 and .01

41) During a test period, an experimental group of 10 vehicles using an 85 percent ethanol-gasoline mixture showed mean CO₂ emissions of 667 pounds per 1000 miles, with a standard deviation of 20 pounds. A control group of 14 vehicles using regular gasoline showed mean CO₂ emissions of 679 pounds per 1000 miles with a standard deviation of 15 pounds. At ? = 0.05, in a left-tailed test (assuming equal variances) the test statistic is:

Solution

(38) Given a=0.1, F(0.05, df1=n1-1=13-1=12, df2=n2-1=10-1=9)= 0.357 (from F table)

F(0.95, df1=12, df2=9) = 3.07 (from F table)

Answer: 3.07 and 0.357

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(40) The p-value= P(t with df=21 <-1.26 ) =0.1107 (from student t table)

Answer: More than .10

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(41)test statistic:

t=(xbar1-xbar2)/sqrt(s1^2/n1+s2^2/n2)

=(667-679)/sqrt(20^2/10+15^2/14)

=-1.6

Answer: -1.645