Let XXX have the MGF MX(t)=(1−2t)−k/2M_X(t) = (1 - 2t)^{-k/2}MX(t)=(1−2t)−k/2 for t<12t < \frac{1}{2}t<21. What is the variance of XXX?
kkk
2k2k2k
k/2k/2k/2
4k4k4k