申論題

6. Suppose that you have just purchased a new battery for your smoke detector, and the life of the battery is a random variable X, with probability density function (pdf) f_x(x) = k✖exp (i.e.,f_x(x) = ke) where x ∈ (0,∞). Assume that t and s are real non-negative numbers.

(c) Find an expression for P(X≥t + s| X≥s).
Answer=__(Q)__.