# Thread: Standard Deviation question

1. ## Standard Deviation question

I know that the standard deviation of X is sqrt of the variance of X.

How do I find the standard deviation of (aX + b) if X has a variance of σ^2?

2. $V(aX+b)=a^2V(X)$ do you want a proof?

So, $\sigma_{aX+b}=|a|\sigma_X$

since $\sqrt{a^2}=|a|$