Enigma 1767: Not over easy
18 September 2013
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From New Scientist #2935, 21st September 2013 [link]
Joe always likes his fried eggs sunny side up. During breakfast in a motel in North Carolina he was given 36 cards, printed on one side with the motel’s name and address, and on the other with two eggs sunny side up. With the cards were instructions to place them on the table one by one and sunny side up to try to make a 6×6 array with all cards sunny side up. As always with puzzles, there was a catch. If, as a card was placed, it touched edge to edge one or more cards, those cards had to be turned over. In solving the puzzle, Joe placed as many cards sunny side up as was possible.
How many did he manage?