JordiGHApparently #JewishProblems aren't as well known as I thought they were:
https://arxiv.org/abs/1110.1556
These were unusually difficult mathematics problems given to Jewish students at Moscow State University circa 1970-1980 in order to keep them out. The problems are fiendish because they can be solved without needing too much specialised knowledge, but the solutions require more cunning than can be developed in the short time of a formal examination.
The problems themselves are very interesting.
Jewish Problems
This is a special collection of problems that were given to select applicants during oral entrance exams to the math department of Moscow State University. These problems were designed to prevent Jews and other undesirables from getting a passing grade. Among problems that were used by the department to blackball unwanted candidate students, these problems are distinguished by having a simple solution that is difficult to find. Using problems with a simple solution protected the administration from extra complaints and appeals. This collection therefore has mathematical as well as historical value.