Sum[ i^2 * (5/6)^i, {i, 1, Infinity}] / Sum[ i * (5/6)^i, {i, 1, Infinity}]

Uh oh! Wolfram|Alpha doesn't run without JavaScript.

Please enable JavaScript. If you don't know how, you can find instructionshere.Once you've done that, refresh this page to start using Wolfram|Alpha.