I need your help on how to start solving this problem. I really have a hard time and do not know where to start. 

Let X1, X2 , … , Xn be a random sample from U(0, a) and let (1), (2), … , () denote the order statistics. The range is defined as = () − (1); the midrange, a measure of location like the
sample median, is defined as = 1/2 (X(n) + X(1). 

a. Derive the joint pdf of and .

b. Derive the sampling distribution of R.

c. Suppose = 1 and = 2. Find the probability that the two observations will not differ by less
than 0.5.