An interesting puzzle
36374
Exercise 1.6.3 from Alon & Spencer's *The Probabilistic Method*: prove that $Pr[|X-Y| \leq 2] \leq 3 Pr[|X-Y| \leq 1]$ for i.i.d. real RVs $X$ and $Y$
156076
Human between two bodies of large mass
111042
A geometry problem from high school Olympiad selection round
46430
A simple decision problem whose decidability is not known
146991
Puzzle question finding Calvin
112596
Stones in a bag with Combinations
37503
chess path combination
2786
The staircase paradox, or why $\pi\ne4$
154867
Bell puzzle in the Temple of Eothas
78163
Hint for problem on $4 \times 7$-chessboard problem related to pigeonhole principle
63454
Lewis Carroll's Pillow Problem via Bayes' Theorem
65372
Triangles defined on an infinite Go board by same-colored stones
70829
Good Mathematical Puzzle Book for Couples
94295
Pigeonhole-principle with two choices
107964
Simple combinatorics problem.
4505
Number of students in school club : $4$ Circles Venn Diagram Puzzle
73323
Permutations when some objects are alike