Math Warehouse, Math Is Fun and Math-Only-Math.com make math puzzles with answer keys. Topics range from basic numbers to algebra, geometry and trigonometry, and the puzzles are available online.
Books featuring math puzzles and answers include "The Moscow Puzzles: 359 Mathematical Recreations" by Boris A. Kordemsky, "Brain Teasers for Kids" by Peter Lloyd and Jennifer Simmons, and "100 Math Brainteasers" by Zbigniew Romanowicz and Bartholomew Dyda. As of January 2016, "The Moscow Puzzles" is Amazon.com's top seller in the math games category. "100 Math Brainteasers" is suitable for seventh through 10th grade levels and covers arithmetic, algebra and geometry brain teasers, puzzles, games, and problems with solutions.
Math.com offers some puzzles on its site, while IXL Learning hones skills from junior kindergarten through 12th grade. The site groups skill areas by grade. Skill areas for 11th grade include evaluating rational exponents, conditionals, graphing linear inequalities, understanding surface and volume, and solving right triangles. Skills for 12th grade include solving quadratic equations by factoring, simplifying complex fractions, solving rational equations, and calculating probabilities.
CoolMath4Kids.com includes fun math puzzles and animated logic puzzles. The puzzles are ordered from easy to difficult to allow students to warm up before the problems get really challenging.