# Joint Bivariate Exponential Distribution

Homework Statement
Consider two components and three types of shocks. A type 1 shock causes component 1 to fail, a type 2 shock causes component 2 to fail, and a type 3 shock causes both components 1 and 2 to fail. The times until shocks 1, 2, and 3 occur are independent exponential random variables with respective rates $\lambda_1, \lambda_2, \lambda_3$. Let $X_i$ denote the time at which component i fails, i = 1, 2. The random variables $X_1, X_2$ are said to have a joint bivariate exponential distribution. Find $P\{X_1 > s, X_2 > t\}$.

The attempt at a solution
This problem would by so much easier if type 3 shocks didn't exists as it would make $X_1, X_2$ independent. Anywho...

Let $Y_1, Y_2, Y_3$ be the times shocks of type 1, 2, 3 occurred. I know I'm going to have to deal with the joint distribution of these three random variables. However, I can't think of anything. I need a little hint.