1. Let X1, X2, X3, and X4 be independent, U (0, 1)-distributed random variables. Compute
(a) P (X(3) + X(4) ≤ 1),
(b) P (X3 + X4 ≤ 1).
2. Let X1, X2, X3 be independent U (0, 1)-distributed random variables, and let X(1), X(2), X(3) be the corresponding order variables. Compute P (X(1) + X(3) ≤ 1).