Let X1,...,Xn(n2) be a random sample from the distribution of the random variable X with an exponential distribution with \underline{mean} >0:

Define the following estimators for :

^1:=1nni=1Xi, ^2:=ni=1Xi, and^3:=37X1+47X2

Which of these estimators are unbiased?

Select one:

^1 and ^3

Only ^2

None of them

All of them