It's a math puzzle designed for third graders, but many adults are having trouble solving it. The puzzle looks something like Scrabble, with a series of boxes that snake up, down and across a page.

The rules of Sudoku dictate that every row, column and 3×3 bolded box in the completed grid must contain the digits 1 through 9 exactly once. A surprising fact emerges from these simple rules. In ...

Imagine that you have three boxes: one containing two black marbles, another containing two white marbles and a third containing one black marble and one white marble. The boxes were labeled for their ...