No point to this oldie-but-goodie, except to warm up your brain cells. Suppose you have an old fashioned balancing scale with two trays. You own 12 coins that look identical. All are equal in weight � except for one that is either heavier . . . or lighter than the others. Your challenge: in no more than three uses of the scale, find the one, uniquely weighted coin . . . regardless of whether it is heavier or lighter than the others. Hint: there is one correct solution.
Please forget the comments section; earlier answers were based on my faulty definition of the problem; and the answers to this revised problem are incorrect. Also, my solution key was too large to fit in the comments section. For the full solution key, just e-mail me at firstname.lastname@example.org.