- Let $X_{i} i=1, \ldots, 50$, be i.i.d. $\chi_{ u}^{2}$-distributed random variables. Find the number of degrees of freedom $ u$ such that the approximate probability $P\left(T_{0} \equiv S_{50) \equiv \sum_{i=1}^{50) X_{i} \leq 100 \sqrt{ u} ight) $ is $0.5$. A1 B 2 B 3 D4 SP.PC.091