Finding the expected value of a probability function

[Jessica21]

1. Suppose X is a random variable with probability function
f(x) = 0.49x(0.3)^ (x-1). Find E(x).



2. E(X) = sum of all x of x*f(x)



3. so I know that E(X) = sum of all x of x*f(x)
so E(x)= 0.49* sum of all x of x^2(0.3)^(x-1)

But I'm not sure how do i evaluate the sum?
Can anyone please help me,thanks!

 

[hgfalling]

Are you sure you have the right probability function? This one doesn't converge on the entire real line and I wasn't able to find an interval where it integrated to 1.

In any event, if you have a random variable X with a probability density function f(x), then the expected value of X is
$$\intop_{-\infty}^{\infty} xf(x) dx$$