刘同学2018-05-21 20:23:38

ABC Company sells computer parts by mail. A sample of 25 recent orders showed the mean time taken to ship out these orders was 45 hours with a sample standard deviation of 12 hours. Assuming the population is normally distributed, the 99% confidence interval for the population mean is: A 45 ± 2.80 hours. B 45 ± 6.98 hours. C 45 ± 6.71 hours. 是不是得有表才能做？2.797是怎么来的？