For the Exponential distribution f(x)=λe−λxf(x) = \lambda e^{-\lambda x}f(x)=λe−λx, what is the value of the mean E[X]E[X]E[X]?
λ\lambdaλ
1λ\frac{1}{\lambda}λ1
λ2\lambda^2λ2
1λ2\frac{1}{\lambda^2}λ21