Odd or Even

Borrow a 50-cent coin from a member of the audience. When it is handed to you, look intently at it for some time, as though you noticed something peculiar about it. Now announce that you will perform an amazing trick with the borrowed coin. Take the coin and, holding it between two fingers of each hand on the back, and the thumb of each hand on the front, bend your hands outwards. At the same time bring the points of the fingers nearer together, and immediately bring them back to their former position. Repeat this motion several times. To someone a little distance away it seems as though the coin is being bent nearly in two at each outward movement of the hand. Place a pile of coins in a clear plastic container and ask a member of the audience to take out a handful. Ask her to check whether she has an odd or even number of coins, but to keep the information to herself. Point out to the audience that she has given you no information, but that you will be reading her mind. Now take a handful of coins out to the container yourself, making sure you leave some behind to rule out the possibility that you counted the coins in advance. Tell the audience that when you add your coins to those of the volunteer, if the number she had taken was even the total will be odd, and vice versa. Drop your coins into an empty container held by another member of the audience, then let your volunteer add hers. Now ask her whether the number was odd or even – and when the coins in the second container are counted, the total number turns out to be the reverse, exactly as you had predicted. The secret: An odd number added to and odd give an even number; if you add an odd number to an even the result is odd. So you only need to ensure that you drop an odd number of coins into the container; if you pick up an even number, use your palming skills to keep back one and hide it in a packet when you get the chance.