9.13Recall that “very satisfied” customers gave the XYZ-Box video game system a rating that is at least 42. Suppose that the manufacturer of the XYZ-Box wishes to use the random sample of 65 satisfaction ratings to provide evidence supporting the claim that the mean composite satisfaction rating for the XYZ-Box exceeds 42. a. Letting represent the mean composite satisfaction rating for the XYZ-Box, set up the null hypothesis and the alternative hypothesis needed if we wish to attempt to provide evidence supporting the claim that exceeds 42.
b. The random sample of 65 satisfaction ratings yields a sample mean of x = 42.954. Assuming that equals to 2.65, use critical values to test versus at each of a = .10, .05, .01, and .001.
z = [ (42.954 – 42) / (2.64 / 65 ] = 2.91
Since 1.28<1.645<2.33<2.91<3.09, reject with =.10, .05, .01, but not with .001. c. Using the information in part b, calculate the p-value and use it to test versus At each of a = .10, .05, .01, and .001
Since p-value = .0018 is less than .10, .05, and .01, reject at those levels of , but not with it ( =.001). d. How much evidence is there that the mean composite satisfaction rating exceeds 42? There is a lot of evidence that the mean composite satisfaction rating exceeds 42.
9.22How do we decide whether to use a Z test or a T test when testing a hypothesis about a population mean? a. Z and T test are used when testing the hypothesis. When the hypothesis uses proportions you use the z test. When the hypothesis uses means you use the T test.
12.10A wholesaler has recently developed a computerized sales invoicing system. Prior to implementing this system, a manual system was used. The distribution of the number of errors per invoice for the manual system is as follows:
REFER TO PG 471
After implementation of the...