Negative Variance I have two independent variables $X$ and $Y$.
$W=X-Y$ when $X\sim \mbox{Bernoulli}\left(1/2\right)$ and $Y\sim N(0,1)$. This puts $\operatorname{Var}(x)=1/4$ and $\operatorname{Var}(Y)=1$, but I have to be misunderstanding something because if $\operatorname{Var}(W)=\operatorname{Var}(X)-\operatorname{Var}(Y)$ then the $\operatorname{Var}(W)$ is negative, which makes no sense. 
What am I missing?

Variance is not a linear mapping. When $X$ and $Y$ are independent (or more generally uncorrelated), $\operatorname{Var}(X+Y)=\operatorname{Var}(X)+\operatorname{Var}(Y)$. Here you should apply this noticing that $X-Y=X+(-Y)$ and $\operatorname{Var}(-Y)=\operatorname{Var}(Y)$.
