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 Jan 9 answered Fixed point of tree automorphism Jan 9 reviewed Approve Polar form of quadratic equations Jan 9 answered Why is Euclid's proof on the infinitude of primes considered a proof? Dec 23 comment Find x, when F(x) is a cdf with given mean and std Right, that does not fully specify a distribution though. Lots of random variables have that same mean and standard deviation but have different distributions and hence would have a different solution for $x$. I'll assume that in this case it is a normal random variable, but in general it could be anything so you should say that it's normal. Dec 23 comment Find x, when F(x) is a cdf with given mean and std is that comma a decimal point in "0,8"? Also, what kind of distribution does $X$ have? Dec 23 reviewed Approve Sequential sums $1+2+\cdots+N$ that are squares Dec 22 answered Why can $y-y_1 = m(x-x_1)$ describe a line but $m=(y-y_1)/(x-x_1)$ is missing a point? Dec 20 answered Wolfram Alpha unexpected answer. Dec 20 comment Show that a continuous function with a certain integral property must be f(x)=x. note that you don't have any assumptions about differentiability so, strictly speaking, integration by parts isn't available to you Dec 17 answered Question on Expected Value, discrete case Dec 17 answered Finding density function for uniform distribution Dec 17 comment “Let $G$ be a planar graph. Show that every pair of vertex-disjoint odd cycles in $G^c$ is connected by an edge.” Can't figure out why “odd” matters. @ErickWong it seems to be in isolation in this case; can you see anything wrong with the proof above? Dec 17 comment “Let $G$ be a planar graph. Show that every pair of vertex-disjoint odd cycles in $G^c$ is connected by an edge.” Can't figure out why “odd” matters. @hbm You're right, I edited it to change slightly. Is what I have now true? Dec 17 revised “Let $G$ be a planar graph. Show that every pair of vertex-disjoint odd cycles in $G^c$ is connected by an edge.” Can't figure out why “odd” matters. added 7 characters in body Dec 17 revised “Let $G$ be a planar graph. Show that every pair of vertex-disjoint odd cycles in $G^c$ is connected by an edge.” Can't figure out why “odd” matters. added 27 characters in body Dec 17 revised “Let $G$ be a planar graph. Show that every pair of vertex-disjoint odd cycles in $G^c$ is connected by an edge.” Can't figure out why “odd” matters. added 2 characters in body Dec 17 asked “Let $G$ be a planar graph. Show that every pair of vertex-disjoint odd cycles in $G^c$ is connected by an edge.” Can't figure out why “odd” matters. Dec 17 awarded Good Answer Dec 16 awarded Mortarboard Dec 16 comment Monty hall problem extended. To add to this answer a little bit, consider the case with $n$ doors where Monty opens each of the remaining doors except for 1 (another, different generalization of the original problem to OP's). Then, again, if you don't switch your probability of winning is $\frac{1}{n}$, and if you do switch, your probability of winning is exactly equal to the probability that you chose incorrectly at first (this is identical to the case with 3 doors). Then your probability of winning is $\frac{n-1}{n}\rightarrow 1$ as $n\to\infty$, so in this case, Monty's help is incredibly useful.