Exercise 2.18: Random variables X1 and X2 are independently and identically distributed with p.d.f. f(x) = Ae^(-x), x ≥ 0. Given that the p.d.f. of X1 + X2 is A^2e^(-4x), show that the distribution of X1 conditional upon Z = z is the uniform distribution on (0,2). Prove that the MVUE of Pr[X1 > 1 | X2 = e] is e^(-1) if X2 < 1, and e^(-2) if X2 > 1.