# Math Help - expected value of a monotonic function of a random var.

1. ## expected value of a monotonic function of a random var.

hey,
say I know that the following is true:

$E(X)=k$

(where E(.) is the expected value, X is a positive random variable and k is some positive and final number)

what can I say about $E(log(X))$ ?

Can I say it is also final, for instance?

I can maybe even assume k>1 , if it helps (but I cannot assume that on X, which I guess could've helped more in this case)

thank you

2. ## Re: expected value of a monotonic function of a random var.

I'm not sure what you mean by 'final' number? If you mean terminating number, then no. Consider, for example, a trivial pmf where x=2 with probability 1.