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Homework Help: Normal distribution

  1. Jul 14, 2009 #1
    1. The problem statement, all variables and given/known data
    Assume x is normally distributed with a mean of 5 and standard deviation of 4. Determine value of x that solves:
    P(-X<x-5<X) = .99

    2. Relevant equations
    I have been using normalCDF and inverse functions on the TI-84 to solve, and I understand how to do these without the calc as well using the standard (x-mean)/stand dev techniques.

    3. The attempt at a solution
    I have a good understanding of how to work the general problems as this is the last one out of 50 I have solved. The issue is how to start this one? The teacher left a mysterious hint: Distribution?
  2. jcsd
  3. Jul 14, 2009 #2


    Staff: Mentor

    From the probability above, what you want to solve for is X, not x.
    You know that your random variable X is n(5, 4). If you let Y = X - 5, how is Y distributed? What would you need to do to get a probability involving Z, the standard normal n(0, 1) random variable? How should your original probability be rewritten so that it involves Z (and from which you can get the values you need from a table or maybe your TI?
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