(C)Tetsuya Miyamoto/Gakken

Numbers are a universal language. Following the success of Sudoku, the popular numbers game that originated in Japan, puzzle makers have created a series of new math puzzles to test people's number skills. Lots of kids don't like studying arithmetic or math, but because these games are both fun and educational, they offer even these kids the chance to become math whizzes.

A big KenKen puzzle with the solution

(C)Tetsuya Miyamoto/Gakken

The hottest math puzzle these days is KenKen, known in Japan as "the puzzle that makes you smart." KenKen enables kids to improve their arithmetic skills; moreover, it can help them to pass school entrance exams. More than 1 million copies of this popular series of puzzles have been sold in Japan, including versions made for the Nintendo DS handheld console. The game was first introduced outside Japan in 2007, and it soon became popular. Translated versions were published in Germany, France, the Czech Republic, and other countries. English versions soon appeared in Britain and the United States. The puzzles are set to hit China in autumn 2009. You can play KenKen on the Internet, and it's also featured in some newspapers in the United States, Spain, and Denmark, among other countries.

(C)Tetsuya Miyamoto/Gakken

The rules are simple: all you do is write numbers into a grid of squares. But there's a catch: squares are blocked together by solid lines, and one square in each block has a small number printed in the upper corner. The sum, multiple, or other combination of the numbers in that block must equal this small number. Also, each number can only appear once in each column or row.

For example, when you play an adding puzzle on a 3x3 KenKen grid, like the one in the picture, each of the numbers 1, 2, and 3 appears once in each column and row. The puzzle in the illustration is unfinished, but do you see why the numbers are arranged this way? Larger adding grids are even more difficult, because there are more numbers to fit in each row and column, and the sums are harder too.