To test whether there is any difference between mean tire-tread life due to driv

Question

To test whether there is any difference between mean tire-tread life due to driving conditions, fifteen similar cars were each driven under one of three conditions: city, highway, country. The tread wear was then determined for each car. The number of degrees of freedom for the F-test is: In testing for gender differences in online clothing purchases, samples of 40 females and 40 males were surveyed to determine the percent of each who had made online clothing purchases in the last month. If 16% of females and 10% of males responded favorably, which statistical test should be used to test for gender differences? A. a t-test with df = 78 B. a t-test with df = 39 C. an F-test D) a z-test

Explanation / Answer

27) Independent t test used be used here:

Degrees of freedom (df) for the Independent t statistic is n1 + n2 - 2

So, 40 + 40 - 2 = 78

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