A Very interesting door problem
21443
The locker problem - why squares?
141427
unusual ternary operation
103302
How do I make a 1x1x2 piston door that opens when I step on a plate and not the other way around?
107964
Simple combinatorics problem.
46580
Variation on the Monty Hall Problem
78163
Hint for problem on $4 \times 7$-chessboard problem related to pigeonhole principle
140039
The parking problem riddle
27260
Infinite product with sign changes.
4592
Prison problem: locking or unlocking every $n$th door for $ n=1,2,3,...$
34155
Probability Problem with $n$ keys
22876
Is it possible to create an iron door which responds to levers on both sides
139039
Stars and Bars Combinatorics Problem
120709
Maxwell demon : how can the demon move the door without doing any work ?
86067
A Variation of the even-town odd-town problem
140153
Conjectures Involving floor(x)/piecewise continuity with regards to Integration and Differential Equations
149342
Is there a clever solution to Arnold's "merchant problem"?
83841
Mutual Exclusion Problem