Sum of squared standard normals

Z1,…,Z5Z_1,\dots,Z_5 are independent standard normals. What is the variance of ∑i=15Zi2\sum_{i=1}^{5} Z_i^2?

Show hints (2)+
  1. Var of a sum of independents = sum of variances; find Var(Z²) first.
  2. Var(Z²) = E[Z⁴] − (E[Z²])² = 3 − 1 = 2.

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