A random sample of n=25 individuals is selected from a population with μ=20 , and a 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 r 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 α= 0.05.