These 500 puzzles offer the ultimate challenge for solvers who want to pit their wits against crafty conundrums, stretch their mental powers, and sharpen their IQs. The degree of difficulty keeps rising in each of the 20 sections, so work through them in methodical order to find mathematical patterns that seem to reoccur and visual clues that overlap. That helps as the problems get harder, but beware: just when you think you're caught on to the trick, it changes. A chain of numbers is missing one link; figure out what number belongs there. Get a little artistic with another brainteaser: draw the face in an empty box that continues a varying pattern of smiles, frowns, and erased features. It's pure entertainment for the smart set.