To Guess The Missing Figure.
To tell the figure a person has struck out of the sum of two given numbers:—Arbitrarily command those numbers only, that are divisible by 9; such, for instance, as 36, 63, 81, 117, 126, 162, 261, 360, 315, and 432. Then let a person choose any two of these numbers; and, after adding them together in his mind, strike out from the sum any one of the figures he pleases. After he has so done, desire him to tell you the sum of the remaining figures; and it follows, that the number which you are obliged to add to this amount, in order to make it 9 or 18, is the one he struck out. Thus:—Suppose he chooses the numbers 162 and 261, making altogether 423, and that he strike out the centre figure, the two other figures will, added together, make 7, which, to make 9, requires 2, the number struck out.