Henry Ernest Dudeney/Modern Puzzles/100 - Odds and Evens

by : $100$

 * Odds and Evens
 * Here is a little parlour trick, the explanation of which is quite easy.


 * Ask a friend to take an even number of coins in one hand and an odd number in the other.
 * You then undertake to tell him which hand holds the odd and which the even.
 * Tell him to multiply the number in the right hand by $7$ and the number in the left by $6$,
 * add the two products together, and tell you the result.
 * You can then immediately give him the required answer.


 * How are you to do it?


 * In practice, after he had given me the result, I should say,
 * "Let us add your age, now deduct the day of the month," and so on --
 * a lot of absurd apparent calculations merely devised for his mystification,
 * for you already know the answer.