Think of a number of 3 or more figures, divide by nine, and name the remainder; erase one figure of the number, divide by 9, and tell me the remainder and I will tell you what figure you erased.

Method. If the second remainder is less than the first, the figure erased is the difference between the remainders; but if the second remainder is greater than the first, the figure erased equals 9, minus the difference of the remainders.