Twenty male athletes were given a special candy bar daily for several weeks, and each man’s body weight was recorded. It is found that the mean change in body weight was +1.5 kg. Suppose that the 20 data came from a weight-change population with a known variance s^{2 }= 9.95 kg^{2}. State the appropriate null and alternate hypotheses, perform the appropriate statistical test at a = 0.05, and make biological meaningful conclusion for the following situations:
(a) Test whether the candy bar have significant effect on body weight (i.e., the null hypothesis is the body weight change is equal to 0)?
(b) Test whether the candy bar can decrease body weight (i.e., the null hypothesis is the body weight change is not less than 0)?