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 Apr21 comment Distribution Function Of a Random Variable X - Question @SuperRhinocerus, what are you studying? Apr20 comment A store is offering a 20% discount on a certain item. The store’s sale of the item is subject to a 6% sales tax. no problem glad to have helped :) Apr20 comment A store is offering a 20% discount on a certain item. The store’s sale of the item is subject to a 6% sales tax. correct, the pure tax component itself is 0.06*0.8x, and thus the total amount including tax is 1.06*0.8x, whereas scenario 1 is 0.8*1.06x, which is equal. Apr18 comment Find the height of statue. @ClaudeLeibovici, yes my assumption was that the height of the observer was insignificant compared to the height of the tower, however without knowing the angles X and Y the validity of this assumption is still in the dark. Apr18 comment Derivation with respect to a derivative Velocity often doesn't depend on position. E.g. if velocity = 4km/hr, you don't need to know the position in space to work out the velocity. But in general it depends on the nature of x(t) whether it is dependent on position or not. E.g. acceleration due to gravity is dependent on position, and thus you would have to apply the chain rule when differentiating. Apr18 comment Deriving a formula for a confidence interval I think you should have a plus sign in the numerator of your pooled variance normally. Consider looking at the Welch t test when variances are not assumed to be equal. Apr18 comment Deriving a formula for a confidence interval What are you studying? Apr17 comment Easy proof of Black-Scholes option pricing formula It's kind of intuitive don't you think? Apr17 comment Need confirmation that the following problem is correct. How about you try 10 different values for alpha in the calculator/excel and see if it always gives 8. If so, then it is very likely that the statement is true. The more values you try, the more likely you can reject the null hypothesis that the statement is false. Apr17 comment Find distance between two poles. How is tan(ACB) = AB/BC. The angle ACB is not even part of a right angle triangle given the way you have described the situation. Apr17 comment Is it valid to get a correlation between moving averages? I think it is fine to use the moving average, as while each day data point will be used 10 times, each moving average data point only counts 1/10th of this, and effectively with a large data set the moving average should yield the same correlation as a day by day analysis. I say a large data set because the first 9 data points won't be counted a full 10 times, nor the last 9 data points, so provided you have much more than 18 moving average data points you should be ok. Apr17 comment How sample size affects confidence interval. In this example, sigma is the population standard deviation, and thus is independent of sample size. So your answer is correct. Technically however your working should be 1.96sigma/sqrt(n) is the margin error, but the 1.96 cancels out anyway. Apr17 comment Simple interest problem @Al.Ka, my belief is that the best way to teach is by direct instruction. If a student sees enough well worked examples, they will learn to emulate that over time. Apr17 comment Simple interest problem @Larry, what about my answer, I answered first. Apr4 comment When will one maximum turn into three maximums? @ClaudeLeibovici, by distinct, I mean when there exists three maximum solutions to the equation y'(x) = 0, as opposed to x = 0 being the only such solution. Apr4 comment Using CLT to calculate probability question What is the "right answer" ? Apr4 comment How to solve this equation for x? $0 = (x+k)e^{-(x+k)^2}+(x-k)e^{-(x-k)^2}$ @Winther, can you help me with this similar quesiton: math.stackexchange.com/questions/1219657/… Apr4 comment How to solve this equation for x? $0 = (x+k)e^{-(x+k)^2}+(x-k)e^{-(x-k)^2}$ @ClaudeLeibovici, I was more interested in whether there was a way to manipulate to find x, rather than the solutions themselves. Claude are you able to help on this queston: math.stackexchange.com/questions/1219657/… Apr4 comment How to solve this equation for x? $0 = (x+k)e^{-(x+k)^2}+(x-k)e^{-(x-k)^2}$ @Winther, yes I was able to figure that one out. Apr4 comment How to solve this equation for x? $0 = (x+k)e^{-(x+k)^2}+(x-k)e^{-(x-k)^2}$ @Winther, yes there should be 3 solutions for x. One is x = 0 and the other two depend on the value of k.