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Homework Help: Standard Deviation Problem

  1. Oct 31, 2009 #1
    1. The problem statement, all variables and given/known data
    http://img338.imageshack.us/img338/5064/picture1nk.png [Broken]

    2. The attempt at a solution
    I know the area for -1.5 is .0668. I also know that the area of the positive half of the curve is .5000. I don't know how to figure out what the other blue piece is or how much the white space is worth.
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Oct 31, 2009 #2


    Staff: Mentor

    Since all they give you in the problem is x = -1.5, my guess is that you're supposed to find P(x < -1.5) and P(x > -1.5), and just assume that the white region is essentially not there.

    On the other hand, I can see little tickmarks in the drawing, so maybe you're supposed to assume that they are at -1.5 and -1.25. Under this assumption you would be finding P(x < -1.5) and P(x > -1.25). Whichever way you decide to go, be sure to include your assumptions.

    Regarding your other question, and assuming we want to find P(x > -1.25), the area under the curve between x = -1.25 and x = 0 is the same as the area between x = 0 and x = +1.25. Can you find that area/probability? Whatever that is, add it to the .50 you already have and your will have P(x > -1.25).
  4. Oct 31, 2009 #3


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    Science Advisor

    You are apparently given that the left boundary of the white (unshaded) region is -1.5. If you do not know the x-value for the right boundary, there is no way to answer this.

    (I might be inclined to make a guess of x= -1, but that should be given in the problem.)
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