barrycarter
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 Mar 30 comment Probability of having $k$ similar elements in two subsets. I think you're right. To find this formula, I basically looked at all (2^n)^2 ways of choosing two subsets. Are you saying that, for a given subset S, I shouldn't have counted (S,S) twice? I thought of this problem as randomly selecting one subset and then randomly selecting another. Do you think I've overcounted? Mar 29 answered Probability of having $k$ similar elements in two subsets. Mar 29 comment Probability of having $k$ similar elements in two subsets. Do you mean how I got there or what $n$ and $k$ mean? Mar 29 comment Probability of having $k$ similar elements in two subsets. I believe this simplifies to my answer, could you check? Mar 29 comment Calculate the coordinates of two points in an isosceles triangle I'd be happy to help you in real time for free (see my contact info), but I will expect you to learn, and won't just give you the answers. Mar 28 comment Probability of having $k$ similar elements in two subsets. $4^{-n} 3^{n-k} \binom{n}{k}$ Mar 28 comment Does the method of substitution always work for solving linear congruence systems? I think I'm missing something. Saying that x=1 (mod 5) and that x = 1+5k for some integer k are exactly the same thing. That's pretty much the definition of modulo. Mar 28 comment Is the computation of this limit of distributions done right? I'm missing something very basic here. Isn't i*0 equal to 0? Mar 28 comment Function of two Random Variables using Inverse Transformation Since the cdf is the integral of the pdf, my first thought would be to use integration by parts or something similar. Mar 28 comment Finding angle between y axis in two rotated coordinate systems I'm missing something. Do you get to choose the vector whose coordinates you can measure? If so, choose the y axis. If not, and if it's a rigid rotation, then the angle change will be the same for all vectors, so just measure the angle change in your given vector, and that'll also be the angle change for the y axis. Mar 28 comment Composition of convex and concave functions Is $x^T$ the transpose of $x$? Are we dealing with complex numbers here? Mar 28 comment Probability for At Most Events I suspect the pigeonhole principle will come into play at some point. Mar 28 comment Board game probability I think this question is fine here, as it's about combinatorics. However, a few more specifics: do the numbers have to appear in the specified order? Are the three combinations you gave the only possible ones or are there others? Show us at least a little of what you've done so far. Mar 28 comment Gamma functions and Binomial Sums You may also want to look at en.wikipedia.org/wiki/Pochhammer_symbol ... then again, maybe not. Mar 28 comment Finding a function to map from logical to physical addresses $4 \left\lfloor \frac{x}{12}\right\rfloor +(x \bmod 4)$ would be my first guess. Mar 28 comment finding the standard matrix for the transformation. As the problem suggests, find where the two unit vectors (0,1) and (1,0) end up and then build the matrix from that (the matrix is literally the transformation of the unit vectors). Mar 28 comment Interquartile range from a step and leaf diagram Hint: convert the step and leaf diagram to a list of numbers. Mar 22 comment use of wolfram in determining area between two curves OK, I took a quick look and WA now officially sucks. In your first link, the area $\left| x \right|>4$ under the curve isn't shaded in. This is technically correct (x=3 y=4 is on the curve) but the curve goes beyond this, appearing to show that x=5, y=3 is also a solution. Sadly, WolframAlpha has declined significantly in quality since they decided to create a registration required (and non-free?) 'pro' version. My advice is: stop using it (sorry!). I also just realized the curve touches y=10, x=0. They've drawn a circle of radius 10, not radius 5. Mar 22 comment use of wolfram in determining area between two curves @jim LOL :) Yeah, I don't think we can dismiss that one as a scale issue :) Mar 22 comment Simulation missiles - initialization vector Your formula looks correct for transforming spherical coordinates into Cartesian coordinates, so I think you're OK.