Let a person select a number greater than 1 and not exceeding 10. I will add to it a number not exceeding 10, alternately with himself; and, although he has the advantage in selecting the number to start with, I will reach the even hundred first.
Method. I make my additions so that the sums are 12, 23, 34, 45, etc., to 89, when it is evident I can reach the hundred first. With one who does not know the method, I need not run through the entire series, but merely aim for 89, and when the secret of this is seen aim at 78, then 67, etc.