The two information theoreticians from puzzle 19 now attempt an even more ambitious trick. It is in fact the same trick, but performed this time with a pack of 124 cards! How does this trick work?
(Note: 124 cards is the maximum number of cards for which this trick can be performed. The cards may be thought of as four suits with 31 cards each, or perhaps as days from a calendar, using the months January, March, May, and July. Or they may be thought of as a double deck, with 20 extra cards from a third deck thrown in, bearing in mind that the magicians must be able to tell, perhaps from the design on the back of the cards, from which pack a given card is taken. Or they may simply be numbered from 1 to 124.)
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