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jin ha

Apparently, this user prefers to keep an air of mystery about them.

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  • Member for 7 years, 4 months
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  • Last seen Oct 30 '13 at 1:09

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7 Prove that $\sum_{k=0}^{m}\frac{\binom{m}{k}}{\binom{n}{k}}=\frac{n+1}{n+1-m}$ Oct 18 '13
2 Problem of color painting on a circle. Oct 18 '13
2 Find a closed expression for the sum of the entries of the Pascal triangle inside the upper n x n rhombus. Oct 19 '13
2 Given n = 4k. Prove that $\sum_{i=0}^{2k}\binom{n}{2i}(-1)^i=2^{2k}(-1)^k$. Oct 21 '13
2 Two soccer team players sit at a round table question. Oct 21 '13
1 Is $Cov(X,|X|)=VarX$ when $X\sim \{-1,0,+1\}$? Oct 22 '13
1 Sources for summation topics Oct 19 '13
1 Find the number of 6-digit odd numbers that do not contain two consecutive fours. Oct 19 '13
1 use combinatorial reasoning to calculate $ \sum{\binom{100}{a}\binom{200}{b}\binom{300}{c}}$ Oct 18 '13
1 Prove $\sum_{k=0}^{n}(-1)^k(k+1)\binom{n}{k}=0$ Oct 18 '13
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