#math/probability #TODO Variance is a numerical measurement describing how far a set of numbers are spread out from their average (mean). $ \text{Var}(X)=E[X^{2}]-E[X]^{2} $ https://chatgpt.com/c/6a9695b5-4d30-83e8-80a5-6f58ed15a05c **Derivation**: The spread of a sample $X_{i}$ from its average $\bar{X}$ is given by $|X_{i}-\bar{X}|$. We want to penalize things that further away more so we square the value to $|X_{i}-\bar{X}|^{2}$. Across all the samples, this is calculated as the expected value of $\sum _{k=1}^{n} \frac{ |X_{k}-\bar{X}|}{n}$.