# Math Help - Expectation and variance

1. ## Expectation and variance

I'm a little confused with this distribution.

$r_{i,j} = \sqrt s\{-1 with probability \frac{1}{2s}, 0 with probability 1-\frac{1}{s}, 1 with probability \frac{1}{2s}\}$

I see that the expectation is 0, but how do I derive the expectation and variance?

2. what does i and j have to do with the right hand side?