translation: And so this is one thing to realize: if you take the probabilities of heads plus the probabilities of tails, you get one half plus one half, which is one, and this is generally too: the sum of the probabilities of all of the possible events should be equal to 1, and that makes sense, 'cause you're taking, you're adding up all of these fractions, the numerator and then add up to all of the possible events the denominator is always all the possible events, so you'll have all the possible events over all the possible events when you add all of these things up.
translation: Và đây là thứ cần để ý. Nếu bạn lấy xác suất mặt ngửa cộng xác suất mặt sấp, bạn được 1/2 cộng 1/2, nghĩa là 1. Và điều này đúng trên tổng quát.