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A tube with a screw cap contains 50 pennies. One of those pennies has a small label on the face.
While your back is turned, the spectator hides the marked penny some where mixed into the rest of them, noting the number of the position 1-50 and screws the cap on. You pick up the tube but you do not open it. You name the number of the coin! They open the cap and count the coins, and it is in the location they put it in. All may be examined.