IQ Challenge - Tapa dura

More than 500 conundrums, mind-benders, and mathematical teasers will help puzzle fans push their IQ levels to the maximum. Visualize this collection as a ladder into the stratosphere of intelligence: 20 levels of ascending difficulty each contain a variety of numerical and alphabetical questions that tease and stimulate the brain. Start from the beginning, with Level One, and work methodically through to the end. Think logically, rationally, and laterally when unraveling these tangled mental knots, and watch for emerging patterns that make solving the later problems easier. Resist the temptation to look at the answers (all at the end), and when you're stumped, try to look at the puzzle from a different perspective--that's how to sharpen the wits and train the mind.