Sorry, it was a stupid question. You can ignore it. But it was a good LATEX practice for me though.

In the text, for

We have and ; therefore,

I then did that transformation [tex]Y=X-r{/math] to obtain

I then found the MGF to be:

I then tried us use the MGF to find and

and

therefore

So here's my question:

Why does

and

but

Var(Y)=Var(X)?