A random sample of n = 25 individuals is selected from a population with = 20,

Question:

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