Say I have a quiz with 10 questions. There are 5 answers A and 5 answers B (which are the only possible choices). Likelihood of getting a correct answer in a single question is then 50%. What if I knew that there were actually 7 answers A? Would the probability of getting it right for a SINGLE question change to 70%?
I wouldn't mind if You gave me a link to a valuable source as I'm in an argument with somebody.
Yes, if you choose a single question randomly, the probability to get it right is $0.70$. The situation is analogous to picking one red ball from a bag that contains $7$ red balls and $3$ black balls.