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  • 0 posts edited
  • 1 helpful flag
  • 27 votes cast
Feb
5
comment Find the limit of the trignometric function?
I have deleted my moronic comment and enrolled myself in basic arithmetic class ;)
Dec
1
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?
Dec
1
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)
Dec
1
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.
Dec
1
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.
Dec
1
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.
Dec
1
comment Deciphering game formula
You might ask (with the specific game mentioned) at reverseengineering.stackexchange.com
Nov
3
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.
Nov
3
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 :)
Nov
3
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?
Nov
3
comment Confidence Interval for a Mean
For a sample size this small, perhaps use the Student T distribution instead?
Nov
1
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.
Oct
29
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.
Oct
29
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)
Oct
29
comment Elementary matrix proof
Do you mean mu times m if i=l and k=m?
Oct
29
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.
Oct
29
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.
Oct
29
comment Understanding Mathematical Symbols in Algorithms
I think it means T(i,j)=0 when j<i. I read it as "for all i and j, when j<i".
Oct
27
comment A question about $f(x)\equiv 0$
Derivative of both sides using product rule and fundamental theorem of calculus for right side? We know g'(x) <= 0 everywhere. That, combined with the fact that a negative times a negative is positive MAY (or may not) help.
Oct
27
comment an example of a sequence $(u_n)_n$ taking its values in $[-1,+1]$ such that $(u_{n+1}-u_n)$ converge to zero but $(u_n)_n$ does not converge
If I understand correctly, you're creating a sub-sequence where u(n) bounces between approximately -1 and approximately 1, and thus never converges, is that correct?