The lifetime in months of a transistor in a certain application is random with probability density function:

f(x) = {0.4e^-0.4x, x> 0 0, x< 0

a. compute the mean lifetime.
b. compute the standard deviation of the lifetimes.
c. compute the cumulative distribution function of the lifetime.
d. compute the probability that the lifetime will be less than 6 months.
e. compute the 60^th percentile of the lifetime.