The mean monthly salary of a random sample of 20 college graduates under the age of 30 was found to be $ 3120 with a standard deviation of $677.Assume that the distribution of salaries for all college graduates under the age of 30 is normally distributed.

7. Construct a 90% confidence interval for  , the population mean of monthly salaries of all college graduates under the age of 30.

a) (1408, 4831) b) (1058, 1582) c) (1071, 1569) d) (2858, 3381) e) (2741, 3498)

8. all other information remaining unchanged, which of the following would produce a wider interval than the 90% confidence interval construct above?

a)A sample of size 28 instead of 20 b) A sample of size 24 instead of 20 c) An 80% confidence interval rather than a 90% confidence interval d) A sample with a standard deviation of 525 instead of 677 e) A sample with a standard deviation of 725 instead of 677