Alright, I can see that you specifically ask for a probability in the question you suggested. It is similar to "How likely will this coin show heads if tossed?", which would be 50%. Based on the things we know, we could also calculate my chances of becoming president. Because there are much more aspects to include, this would be very difficult. However, depending on how much we know, the answer is not always the same. Let's say I'd run for the US-president. The fact that I wasn't born in the USA reduces my chances immensely (not to 0% though, because it's not impossible that the rule will change). But if you didn't know that important fact, you would probably rate my chances higher.
What I was trying to say in my text was that probabilities of any kind are nothing but abstractions based on imperfect knowledge. If you ask for the chance of an event to happen, you ask for something that doesn't really exist. No matter what the calculations tell you, determinism suggests that the result (whatever it will be) is certain at any time.