48 views

Substracting two normal distributions [duplicate]

I was wondering if we have two normal distributions of X,Y~N(0,1), why is then X-2Y~N(0,5)? I understand the mean of the X-2Y distribution, but why is the variance 5?
19 views

Computing SD for function of two RV's in R gives wrong results [duplicate]

I have 2 random variables, all independant, discrete and uniform I want to compute standard deviation for Z = X - Y Here is the R code: ...
234k views

How to 'sum' a standard deviation?

I have a monthly average for a value and a standard deviation corresponding to that average. I am now computing the annual average as the sum of monthly averages, how can I represent the standard ...
31k views

169 views

Sum of variances law

I am currently trying to grasp the concept of Variance Sum Law where variance(x + y) = variance(x) + variance(y) I am not even sure if I understand it correctly ...