Quick EV question

[Falker11]

I just want to know if I did my math correct on this problem. Suppose I have a 25% chance of hitting a winner, and when I hit this winner I get payed 3x my bet. So suppose I am playing $10 bets. I would make 20/4 - 30/4 = -10/4 = $2.50 lost per bet. Is my calculation here correct. If not what did I do wrong?
Falker

[gaming_mouse]

No.

EV = (1/4)*30 + (3/4)*(-10) = 0.

This is a fair bet.

gm

[dtbog]

Original poster is right if the bettor doesn't get his $10 back.

(0.25) * (+$20) + (0.75) * (-$10) = -$2.5

gaming_mouse is right if the payout is actually $40 - i.e., the original $10, plus the $30 prize.

-DB

[SossMan]

Not fair.
you are getting paid 2:1 on a 3:1 shot.