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ithisa
  • Member for 11 years, 5 months
  • Last seen more than 4 years ago
31 votes
2 answers
35k views

Proof that the hypergeometric distribution with large $N$ approaches the binomial distribution.

18 votes
6 answers
26k views

Combinatorial proof of $\sum^{n}_{i=1}\binom{n}{i}i=n2^{n-1}$.

14 votes
1 answer
15k views

Show that triangle-free planar graphs are four-colorable

13 votes
5 answers
9k views

Deducing a probability distribution from its moment-generating function

11 votes
4 answers
3k views

Seating of $n$ people with tickets into $n+k$ chairs with 1st person taking a random seat

8 votes
4 answers
236 views

Contradiction in the rules regarding determinants and row operations?

8 votes
2 answers
1k views

Proving that a "prime graph" is connected

7 votes
4 answers
2k views

Is probability and the Law of Large Numbers a huge circular argument?

7 votes
1 answer
2k views

Proving that G contains a cycle with at least $k+1$ edges

6 votes
2 answers
2k views

Expectation score of multiple choice test

6 votes
2 answers
816 views

Interesting probability question about islands and bridges

6 votes
1 answer
1k views

What's so special about a 2D plane in graph theory?

5 votes
3 answers
359 views

Finding a planar graph satisfying these properties

5 votes
2 answers
11k views

Proving that similar matrices have identical ranks

5 votes
3 answers
128 views

No idea how to prove this property about symmetric matrices

5 votes
1 answer
362 views

Proving a property about Gauss-Seidel

5 votes
1 answer
258 views

Strange graph theory problem

5 votes
3 answers
5k views

Proving an identity with a combinatorial proof: $\binom{n}{k}\binom{k}{r}=\binom{n}{r}\binom{n-r}{k-r}$

5 votes
3 answers
258 views

Weird $3^n$ in an identity to be combinatorially proved

4 votes
2 answers
3k views

Biased random walk away from cliff

4 votes
2 answers
145 views

How does this "combinatorial proof" work?

4 votes
2 answers
2k views

Proof using natural deduction

4 votes
2 answers
13k views

Differentiating an infinite sum

4 votes
1 answer
2k views

Proving that a planar graph is bipartite [duplicate]

3 votes
2 answers
3k views

Proving a fact about 4-regular graphs

3 votes
2 answers
97 views

Completely baffled by this question involving putting matrices in matrices

3 votes
3 answers
5k views

Probability problem in textbook

3 votes
2 answers
187 views

Is this proof correct? Textbook has no solution.

3 votes
1 answer
231 views

Why was I wrong doing this problem?

3 votes
4 answers
535 views

Proving $q\Rightarrow r \models (p\land q) \Rightarrow (p \land r)$ using only natural deduction.