Best definition
X-Rated Algebra
Math questions with a hidden mature content, which may sound illogical at first sight, but are nevertheless “sensibly solvable.”

An x-rated algebra question that went viral many years ago is: “Maya is 21 years older than her son Raju. In 6 years, Maya will be 5 times as old as Raju. Where was Maya’s husband?” Answer: On top of his wife—the baby will be out in about a year (x = –1).

via giphy