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 Feb5 comment Find the limit of the trignometric function? I have deleted my moronic comment and enrolled myself in basic arithmetic class ;) Dec1 comment Probability of correctly guessing student number with checksum? The obvious answer would be 1/11. Since 11 is prime, the sum you describe should cycle through all values of sum%11 equally. Just to clarify, you mean the last digit is chosen so the entire sum is a multiple of 11, correct? What do you do if the last digit needs to be 10? Use "X" like they do for SBN/ISBN numbers? Dec1 comment finding n in binomial distribution The Student T distribution might be helpful here (the sample size is too small to use the normal approximation, which yields the (incorrect) result that the size of n is irrelevant) Dec1 comment One difficult integral My approach would be to rewrite log((1-x)/(1+x)) as log(1-x)-log(1+x) and then expand the cube. This will at least break the integral up into smaller chunks. Dec1 comment conditional probability that 5 red balls were placed in the bowl at random This is a trick question. The chance that the remaining 3 balls are red is independent of the colors of the balls you already chose. Dec1 comment Minimum value of an integral with least square? Possible hint: when the integral reaches its minimal value, its derivative is 0. That plus the fundamental theorem of calculus might help. Dec1 comment Deciphering game formula You might ask (with the specific game mentioned) at reverseengineering.stackexchange.com Nov3 comment Conceptual question on showing properties of the absolute value function on $\mathbb{Q}$ OK, I might be misunderstanding the question, but if |a|=0 then a=+0 or a=-0, which are the same thing. I don't see this as a rational number question. It's true for natural numbers, integers, real numbers, and complex numbers as well. Nov3 comment Confidence Interval for a Mean Nah, I'm bad about upvoting other people's answers to my questions, so I feel bad about getting upvotes :) Nov3 comment Conceptual question on showing properties of the absolute value function on $\mathbb{Q}$ Could you show us a more complicated example that doesn't have a simple proof like this one? Nov3 comment Confidence Interval for a Mean For a sample size this small, perhaps use the Student T distribution instead? Nov1 comment Properties of continuity You can also do this directly: to prove continuity at a point k, take c=k-epsilon and d=k+epsilon as epsilon approaches zero and then apply continuity. Oct29 comment Normal Distribution and Cofffee Remember, you're looking at cumulative probability, not just the probability at a specific integer. Add the probabilities (starting with x=3) until the exceed 0.5. There's actually probably a better way of doing this, but this method will work too. Oct29 comment Normal Distribution and Cofffee Hint: you're looking for 3 or more successes (well, failures, but still) in n attempts, where each success has a 1% chance. Use either the binomial distribution (or the normal approximation to it) to find the value of n where the probability is right around 0.5. Other hint: 3 or more successes = the opposite of 0, 1, or 2 successes (might be easier to compute) Oct29 comment Elementary matrix proof Do you mean mu times m if i=l and k=m? Oct29 comment Torn between plugging back into the original vs. an intermediate equation… OK, I think I see what you're asking: if you solve the simpler equation, will all of those solutions still solve the original equation. In this case, they do, but, in general, they might not. In particular, if the simpler equation is itself quadratic (or quartic, etc), the simpler one may give you extraneous roots. So, yes, you need to check that the simpler equations solutions still work with the original equation. Oct29 comment Torn between plugging back into the original vs. an intermediate equation… I prefer plugging into y=3x-1, because you avoid the "extraneous roots" you'd get by plugging into the original. Oct29 comment Understanding Mathematical Symbols in Algorithms I think it means T(i,j)=0 when j