. Suppose that lifetimes of two partsX1andX2are independent exponential random variables with mean rates of1and2, respectively. \[ f(x)=\lambda \exp (-\lambda x) \text {, when } x>0 \text { but } 0 \text {, otherwise. } \] Suppose the system is configured such that the parts are connected in parallel. Let Y=max(X1,X2). Derive the probability mass (density) function of Y.