A random sample of n = 25 individuals is selected from a population with u = 20, and treatment is administered to each individual in the sample.  After treatment, the sample mean is found to be M = 22.2 with SS = 384. 

a. How much difference is there between the mean for the treated sample and the mean for the original population?  (Note; In a hypothesis test, this value forms the numerator of the t statistic.)

b. If there is no treatment effect, how much difference is expected between the sample mean and its population mean?  That is, find the standard error for M. (Note:  In a hypothesis test, this value is the denominator of the t statistic.) 

c. Based on the sample data, does the treatment have a significant effect? Use a two-tailed test with a = .05.