Determine and present result based on set probabilities?

Hi,

I'm making a simple experiment where a person gains or loses several dollars based on what item on the screen they choose. If they choose item A, there's an 80% chance of them winning $10, if they choose item B, a 20% chance of winning $10, etc. I'm trying to start with an if statement, but not sure how to take the percentage and possible outcome, calculate if they will actually win or not, and then display that result. Any help would be appreciated! P.S. - I'm using Psychtoolbox.

Thanks.