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Finding the prob. in a continuous uniform distribution (z values)

  1. Mar 21, 2012 #1
    1. The problem statement, all variables and given/known data

    lBmU6.png

    2. Relevant equations

    0XQcA.png

    3. The attempt at a solution

    I understand that all i need to do is plug these two points into the formula and subtract to get the correct area, but i am not provided a mean or variance as i normally am, so i'm at a loss.
     
  2. jcsd
  3. Mar 21, 2012 #2

    Office_Shredder

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    What does that formula for Z have to do with the original question? Do you know what the definition of a uniform distribution is (i.e. can you write down the density function)
     
  4. Mar 21, 2012 #3
    Here's what we are given in one of the examples helping to explain it to us.

    iOwBU.png

    I put in the formula for Z because if i had the standard deviation and mean, this would be extremely simple (for me)
     
  5. Mar 21, 2012 #4

    LCKurtz

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    Office_Shredders gentle question is a hint that the normal distribution has nothing to do with the problem. Try answering the questions he posed.
     
  6. Mar 22, 2012 #5
    In addition to this, since the distribution in question is uniform, I suggest to draw a picture :-) In this case it would be very self-explanatory.
     
  7. Mar 22, 2012 #6
    OK, so this isn't helping yet, i'm still under the impression that in order to solve this problem, i need the mean (which i'm assuming is 3), and the standard deviation from the mean (which i'm at a loss for). Anyone able to help explain this better, it's the first question in my homework and i feel i'm just over thinking it?
     
  8. Mar 22, 2012 #7

    LCKurtz

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    Why are you assuming the mean is 3? Don't you know how to calculate the mean?

    1. What is the density function for this problem?
    2. What is the formula for the mean? Does it give 3?
    3. What is the formula for variance? What does it give?

    Show us some work. And, as an aside, are you sure calculating the mean and variance is what you need for this problem? What is the formula for P(A|B)?
     
    Last edited: Mar 22, 2012
  9. Mar 22, 2012 #8
    I'm assuming the mean is 3 because it is a uniform distribution 1 through 5, which would make the mean three... right? (two units on each side, central tendency). I don't have any more information about this problem than is given, but since it is a normal uniform distribution, it should fit into this distribution:

    ctMCS.png

    I don't have formulas for the mean or variance, alls i have a proofs that the expected value of (x) is the mean, and the expected value of (x minus the mean squared) is the SD.
     
  10. Mar 22, 2012 #9
    Great, i finished the sections homework without any issues, took no time at all, except for this one problem, I must be over thinking it...?? this problem seems like it should be so simple.
     
  11. Mar 22, 2012 #10

    LCKurtz

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    Yes, it would be simple if you would just answer the questions I and others have asked. Why do you keep mentioning the normal distribution, even after you have acknowledged it is a uniform distribution???

    Among other suggestions, I have highlighted in dark blue two questions you have ignored. Answering those two questions is necessary to proceed. And to answer what the density function is, I mean a formula.
     
    Last edited: Mar 22, 2012
  12. Mar 22, 2012 #11
    ahhhh, for some reason i was thinking this was a bell curve the whole time. But, because of that realization, i found the formulas for mean and SD, and plugged them into the formula originally given. Sorry the quality is terrible, but here's what i got.

    XnQ1S.jpg
     
  13. Mar 22, 2012 #12

    Office_Shredder

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    You keep going back to thurs formula for normal distributions, but you don't have a normal distribution.

    I think maybe a more basic question is in order: what's the definition of a density function?
     
  14. Mar 22, 2012 #13

    LCKurtz

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    And he still hasn't give the formula f(x) for the density or the formula for P(A|B). Rogo0034 if you can't answer those two questions you need more help than I can give you. I'm sure they are in your textbook.
     
  15. Mar 22, 2012 #14

    HallsofIvy

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    Do you know what a uniform probability distribution is?
     
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