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Four Corners (Posted on 2004-07-17) Difficulty: 3 of 5
On each corner of a square is a quarter. Your task is to have all four quarter heads-up or tails-up at the end of a turn.

You are blindfolded at the start, and you do not know which are heads-up and which are tails-up. Each turn, you may flip however many of them you want and then ask if you are done (and no, you cannot tell, by touch, whether it is heads- or tails-up). The square is then rotated a random, undisclosed number of quarter spins (multiple of 90 degrees), and you may take another turn.

Minimize the maximum number of turns required to be assured you will complete the task.

No Solution Yet Submitted by red_sox_fan_032003    
Rating: 4.2500 (8 votes)

Comments: ( Back to comment list | You must be logged in to post comments.)
7 moves plus 1 to see if it started solved Comment 7 of 7 |

i guess it would still be 8 turns since the 7 solution doesn't work if the coins all start out solved which could be the case and you didn't know when you started flipping.

the first move should always be flip 0 (or all 4) coins

then the 7 solution is good


  Posted by tanx on 2005-11-07 18:45:05
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