Several recent studies have suggested that people who suffer from abnormally high blood pressure can benefit from

Question:

Several recent studies have suggested that people who suffer from abnormally high blood pressure can benefit from regular exercise. A medical researcher decides to test her belief that walking briskly for at least half an hour a day has the effect of lowering blood pressure. She conducts a small pilot study. If results from it are supportive, she will apply for funding for a larger study. She randomly samples three of her patients who have high blood pressure. She measures their systolic blood pressure initially and then again a month later after they participate in her exercise program. The table shows the results.
a. Explain why the three before observations and the three after observations are dependent samples.
b. Find the sample mean of the before scores, the sample mean of the after scores, and the sample mean of d = before - after. How are they related?