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Dec
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Dec
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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
23
revised Area swept out by non-solar focus not same over equal time?
answer
Nov
22
asked Area swept out by non-solar focus not same over equal time?
Nov
8
comment Norm in R^2 in which norm(abs(x)) != norm(x)
@Martín-BlasPérezPinilla OK, so you're saying norm(a) means a is a member of R^2 whereas abs(a) means a is a member of R? I think you're right. I was treating (x,y) in R^2 as x+i*y
Nov
8
comment Norm in R^2 in which norm(abs(x)) != norm(x)
@Martín-BlasPérezPinilla But the norm is also a real number. To answer this, I'd have to look up the definition of norm, and see if something like max(x,y) counts. However, I'm too lazy to do this :) Or did you mean that you can only take the absolute value of real numbers, not points in R^2?
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
2
comment Working out percentage from Normal Distribution
(1-0.8849) is the probability of z>=1.2, not z<=1.2
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
30
revised Normal Distribution and Cofffee
correct answer + more help
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.