What is the chance you will get aids from somebody that is infected, the first time you have unprotected sex with them?

Depends: That depends on what kind of sex you have, the individual's viral load, and too many other factors to list. Giving you a number is not possible or helpful. Remember that every HIV infection comes from a single encounter, which in some cases can be the first or only encounter with that individual. However, the chances of becoming infected increase with multiple encounters.