Bob tests the null hypothesis that the population mean is less than or equal to 45. From a population size of 3,000,000 people, 81 observations are randomly sampled. The corresponding sample mean is 46.3 and sample standard deviation is 4.5. What is the value of the appropriate test statistic for the test of the population mean, and what is the correct decision at the 1 percent significance level? 高頓網(wǎng)校免費題庫>>
　　A. z = 0.29. and fail to reject the null hypothesis
　　B. z = 2.60. and reject the null hypothesis
　　C. t = 0.29. and accept the null hypothesis
　　D. t = 2.60. and neither reject nor fail to reject the null hypothesis
　　Answer:B
　　B is correct. The population variance is unknown but the sample size is large (>30). The test statistics is:
　　z = (46.3- 45)/(4.5/(sqrt(81)) = 2.60. Decision rule: reject H0 if z(computed)> z(critical). Therefore, reject the null hypothesis because the computed test statistics of 2.60 exceeds the critical z-value of 2.33.