3. Lifetime in years of certain device is exponentially distributed random variable T{ l ). Probability that T > 6 is e 3,P( T > 6) = e 3. a) Find expectation in and standard deviation {IT for given distribution. The system consists of 4 devices of such type and is in working condition if all of its components are in working condition. What is the density function of random variable S, lifetime of system ? What is cumulative function of random variable S ? Find the probability that system that it will not fail a) in the first 3 years? b) in the next 3 years given that it didn't fail in the rst 3 years? c) Find the probability that system's lifetime S satisfies inequality: l