It is you can say a magic trick of mathematics. If I am free to ask questions to the guesser, I would ask whether the number is a prime or composite number. I can ask that whether the number is even or odd. I can also ask factors concerning the divisibility of the number. Suppose the guessed secret number is 50, if I ask whether it is a factor of 5 or not. It will be yes and, I might succeed in my guess. In this way, if I keep asking about the number, I can go to the nearest guess. Really, my strategy is to ask questions regarding the number from which we can know more about the number.