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   Author  Topic: Random numbers  (Read 3546 times)
Altamira_64
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Random numbers  
« on: Jul 29th, 2013, 6:39am »
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Get two random numbers between 0 and 1. Subtract the smaller from the bigger. What is the probability that the result is <0.3? Is it bigger than the probability it is > or equal to 0.3?
For what number the probability for both cases is the same?
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towr
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Re: Random numbers  
« Reply #1 on: Jul 29th, 2013, 8:56am »
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Nicely chosen parameters. But easy enough when you draw it.  
You have a strip along the diagonal of the square where the difference is less than 0.3, leaving two triangles with side 0.7 at opposite corners, which together add to .72 = .49 chance that the difference is greater than 0.3 So the chance of <0.3 is only just greater than >0.3, by 2%
« Last Edit: Jul 29th, 2013, 8:57am by towr » IP Logged

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Altamira_64
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Re: Random numbers  
« Reply #2 on: Jul 29th, 2013, 11:06am »
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Can you draw this?
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towr
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Re: Random numbers   square.dist.0.3.pdf
« Reply #3 on: Jul 29th, 2013, 11:27am »
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See attachment.
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Altamira_64
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Re: Random numbers  
« Reply #4 on: Jul 29th, 2013, 11:59am »
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Great, thanks!
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EdwardSmith
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Re: Random numbers  
« Reply #5 on: Jul 16th, 2014, 2:16am »
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begin
    for i := 1 to bignumber do
    begin
         a:= random(1);
         b:= random(1);
         if a > b then
                c:= c+(a-b)
         else
                c :=c+(b-a);
     end;
     average := := c/bignumber;
     if average < 0.3 then
     writeln("yes")
end;
 
*** error unknown variable on line 2 ***
« Last Edit: Jul 16th, 2014, 2:37am by EdwardSmith » IP Logged


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towr
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Re: Random numbers  
« Reply #6 on: Jul 16th, 2014, 9:04am »
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Is that pascal?
 
In any case, the answer should be a probability, not "yes" or nothing.
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Grimbal
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Re: Random numbers  
« Reply #7 on: Jul 16th, 2014, 9:34am »
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A pascal program should start with "program <name>;".  But maybe that is optional.
 
I think it is meant as pseudo-code.  The variables are not declared, c is not initialized and there is a suspicious double :=.
 
Anyway, the program computes the average distance between the 2 random numbers, not how often that difference is larger than 0.3.  So it definitely doesn't answer to the question.
« Last Edit: Jul 16th, 2014, 9:35am by Grimbal » IP Logged
towr
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Re: Random numbers  
« Reply #8 on: Jul 16th, 2014, 10:31am »
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on Jul 16th, 2014, 9:34am, Grimbal wrote:
I think it is meant as pseudo-code.
Yeah, but then what's up with the "*** error unknown variable on line 2 *** ", that makes me think some compiler or interpreter threw an error.
 
Quote:
Anyway, the program computes the average distance between the 2 random numbers, not how often that difference is larger than 0.3.  So it definitely doesn't answer to the question.
Maybe if you also had the variance. Tongue
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Grimbal
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Re: Random numbers  
« Reply #9 on: Jul 17th, 2014, 3:12am »
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Yes, the error message also bothered me.
It looks like Edward used an IDE to type it but did not go as far as making it a valid program.
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