Data Support


1 . Records on a fleet of trucks reveal that the average life of a set of spark plugs is normally distributed with a mean 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 1,412 miles. To decide if the sample data support the company records that the spark plugs average 22,100 miles, state your decision in terms of the null hypothesis. Use a 0.05 level of significance. 

2 . A machine cuts steel to length for nails. The mean length of a nail is 43 millimeters. There is concern that the settings of the machine producing the nails have changed. To test the claim, twelve nails (n = 12) were sampled. The mean of the sample is 41.5 and the standard deviation is 1.784. To test the claim at the 0.02 significance level, what is the critical value? 


The following data are from an experiment designed to investigate the perception of corporate ethical values among individuals specializing in marketing (higher scores indicate higher ethical values).   Marketing Managers- 6,5,4,5,6,4   Marketing Research- 5,5,4,4,5,4   Advertising- 6,7,6,5,6,6  

 a) Use a=.05 to test for significant   differences in perception among the three groups.   

b) At the a=.05 level of significance,   we can conclude that there are differences in the perceptions for marketing managers, marketing research specialists, and advertising specialists. Use the procedures in this section to determine where the differences occur. Use a=.05.    

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