Sit & Solve (R) Hard KenKen (R) by Tetsuya Miyamoto
The tougher the KenKen, the better the brain workout: Not for beginners! KenKen uses basic maths operations (addition, subtraction, multiplication, and division) while challenging logic and problem-solving skills. This collection of the popular numerical puzzles, featured in the New York Times, takes solving to a higher, harder level.