A mathematical challenge is a type of PROBLEM that requires the use of mathematical skills to solve. It can involve a variety of topics, such as algebra, calculus, geometry, and trigonometry. The answer to this particular crossword puzzle is 'PROBLEM, ' which is a seven-letter word that describes a task or situation that requires a solution. A mathematical challenge is an example of such a PROBLEM. It requires the use of mathematical knowledge and skills to solve, and can be used to test and improve one's understanding of mathematics.