10-1. Let X1, . . . ,Xn constitute a random sample taken from an exponential distribution with probability density function f (x; θ) = -1

θ e−x/θ , x > 0,θ > 0;

0 elsewhere.

Which of the following point estimators for θ are unbiased:

T1 = X2, T2 = X1 + X3 2

, or T3 = X?

Find the efficiency of T1 relative to T3.