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.

(In reply to re(2): Good start by helen)

Good point.  I assumed...falsely...that the puzzle was in an unsolved state to begin with.  In that case, the first step is required after all.

Posted by Ken Haley on 2004-09-08 01:08:05