The probability 2/3 means that there are 2 events we are interested in (which probability to happen we calculate) and there are 3 total events that may happen. The probability 2/3 is equal to the probability 2/3*2/2=4/6. An possible outcome would be : The probability that the side of the backgammon can be divided with 8 (there are 4 possibilities: 8, 16, 2 and 64).
