If you're being asked, then you know that a bet of Heads will be right 1/3 of the time. So the probability from your perspective is 1/3.
It doesn't make a different if you're only doing it once or a million times. The whole point of probability is to figure out what would happen if you did it a million times so that you use the optimal strategy when it happens only once.
It doesn't make a different if you're only doing it once or a million times. The whole point of probability is to figure out what would happen if you did it a million times so that you use the optimal strategy when it happens only once.