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 Jun 15 comment What is the probability that a boy who knows how to solve $25$ of potential $30$ questions will get at least $8$ of $10$ correct? Jun 15 awarded Critic Jun 15 comment Michael Spivak's Calculus - Chapter 1 Problem 6 In case (iii), an odd exponent will preserve the signs of $x$ and $y$, so $y^n$ must remain greater than $x^n$. Jun 15 answered Writing the pdf for a Gamma Distribution Jun 12 comment Bijective function between lists and sets You can generalize this to a bijection between an $n$-length binary string with $1$ appearing $k$ times and a $k$-element subset $S$ of the set of integers between $1$ and $n$. The bijection (mapping subsets to binary strings) would look like $f(S)=a_{1}a_{2}...a_{n}$, where $a_{i}=\begin{Bmatrix} 0 & i\notin S\\ 1 & i\in S \end{Bmatrix}$. You should be able to see that the number of $n$-bit strings where $1$ appears exactly $k$ times is the same as the number of ways to select a $k$-element subset from $\left [ n \right ]$. Jun 5 answered Combination of trees Jun 4 comment Primal and dual problem (Optimal solution) - Operations research Perhaps this answer to a related question will help. Jun 4 comment Primal and dual problem (Optimal solution) - Operations research Have you learned about complementary slackness yet? Jun 4 awarded Yearling Jun 3 awarded Commentator Jun 3 answered Work Problem that deals with Number of Men, Days, Leaving Jun 3 comment What is the most rigorous proof of the irrationality of the square root of 3? Some answers can be found at math.stackexchange.com/q/64643 and math.stackexchange.com/q/131391 and math.stackexchange.com/q/930486. Jun 2 awarded Teacher Jun 2 comment Probability of Opening a Combination Lock @NotALoner you begin entering all codes whose sum is 8 That sounds like OP is trying to say you remember previous tries. Jun 25 awarded Editor Jun 25 revised What is the intuition behind $P(X={\lambda})\ {\equiv}\ P(X={\lambda}-1)$ for a Poisson distribution added condition that lambda minus 1 be a nonnegative integer Jun 25 comment What is the intuition behind $P(X={\lambda})\ {\equiv}\ P(X={\lambda}-1)$ for a Poisson distribution @nrpeterson Thank you. I'll explicitly add the condition that lambda is a nonnegative integer. Jun 25 awarded Student Jun 25 asked What is the intuition behind $P(X={\lambda})\ {\equiv}\ P(X={\lambda}-1)$ for a Poisson distribution Jan 14 awarded Supporter