Checking to see if i am correct

[midvinter]

A roulette wheel has 18 numbers colred red, 18 colored black, and 2 (zero and double zero) that are uncolored. If you bet 1 unit on the outcome red, then either you win 1 if a red number appears or you lose 1 if a red number does not appear. What is your expected gain?

I am not sure if it is asking for probability or not but my answer ended up being that at .47. Is this correct?

[JohnM]

P(red) = .47 is correct (actually .4736), but this is asking you for the expected value or gain of playing the game.

If you bet 1, and it comes up red, you get 1 back, so a net gain of 0.
If you bet 1, and it doesn't come up red, you lose, so a net gain of -1.

P(red) = .4736
P(not red) = 1 - .4736 = .5263

Expected Value = summation of (x * p(x))

= (.4736 * 0) + (.5263 * -1) = -0.526