# Thread: Transformation of Variables problem (Poisson dist)

1. ## Transformation of Variables problem (Poisson dist)

X is dist. Poisson with mean A, where A is moderately large.

You are given that Y = $\displaystyle X^2$

What is the mean of Y in terms of A?

I know this should be really simple, and I could do it is X was continuous, but how would I approach this, given that X is discrete? I'm sure I'm missing something really obvious here :/

E(Y) = E($\displaystyle X^2$) = ...?

2. Originally Posted by Zenter
X is dist. Poisson with mean A, where A is moderately large.

You are given that Y = $\displaystyle X^2$

What is the mean of Y in terms of A?

I know this should be really simple, and I could do it is X was continuous, but how would I approach this, given that X is discrete? I'm sure I'm missing something really obvious here :/

E(Y) = E($\displaystyle X^2$) = ...?
$\displaystyle Var(X)=E(X^2)-\overline{X}^2$

You know $\displaystyle Var(X)$ and $\displaystyle \overline{X}$

CB

3. Ohhh of course. Thanks