4 The continuous random variable Xhas probability density function k f(x) = X 0 otherwise, where n and & are constants and n is an integer greater than 1. (a) Find & in terms of n. [3] (b) (i) When n = 4, find the cumulative distribution function of X. [3] (ii) Hence determine P(X > 7 |X" > 5) when n = 4. [4] (c) Determine the values of n for which Var(X) is not defined