In (a) you want an approximation to the distribution of . In (b) you need the exact distribution.
a) The Central Limit Theorem says that the limiting distribution of is Normal(0, 1).
In your case , and n = 16.
Use the above approximation to calculate . (You don't really need to do any calculation here because the answer is obviously 0.5).
b) Calculate the exact distribution of by following the outline given in this thread: http://www.mathhelpforum.com/math-he...a-samples.html NB: follows a different distribution in that thread but the idea is the same.
Use the pdf of to calculate the exact value of .