12 numbered pigeonholes and balls
23701
I have a problem understanding the proof of Rencontres numbers (Derangements)
26619
Permutations of word 'mathematics'
60381
101 positive integers placed on a circle
35864
Playing with numbers form $1$ to $n^2$ in an $n\times n$ grid
5801
Combinatorial proof help
140858
Number of ways to choose 6 objects when they are of 11 different kinds
46580
Variation on the Monty Hall Problem
58975
How many rectangles can be obtained by joining four of the $12$ vertices of a $12$-sided regular polygon?
81567
Pigeon hole principle to prove $a-b=9$ in subset.
158381
Distinct balls into distinct boxes
24212
proving how many permutations exist.
102791
pigeonhole principle: at least 1 match/hr for 75 hrs, at most 125 matches, then exactly 24 matches in some interval
20174
Discrete mathematics bit strings
472
In how many ways can $3$ red, $3$ blue, and $3$ green balls be arranged so that no two balls of the same colour are consecutive (up to symmetry)?
14139
$(12)$ and $(123\dots n)$ are generators of $S_n$
54794
British Olympiad; Combinatorics Recursion
80744
What is the number of strings at size $n$ that is constructed from ${a,b,c,d}$ and there is an even num of $a$