Calculating EV AA vs lower pair preflop allin

[Joost1982]

A higher pocket pair versus a lower one has 80% chance of winning when preflop allin. How do I calculate my equity...?

I have $50, villain has $50. I move allin with a pocket pair and he calls with a lower one: (0,8 * $50) + (0,20 * - $50) = +$30 ? Is this correct?