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Math Help - Z Value

  1. #1
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    Z Value

    Let Z be a standard normal random variable. Find the z-value(s) for the following situations.
    a.) the area to the left of z is 0.2119
    b.) The area betwen -z and z is 0.9030
    c.) The area to the right of z is 0.6915
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by dclift View Post
    Let Z be a standard normal random variable. Find the z-value(s) for the following situations.
    a.) the area to the left of z is 0.2119
    b.) The area betwen -z and z is 0.9030
    c.) The area to the right of z is 0.6915
    This is an excersise in inverse table look up, and depends on what table you have.

    Lets assume that you have a table of the cumulative standard normal, which
    gives the area to the lef of z-values from 0 upwards, so these probabilities
    are all greater than 0.5.

    In a.) the probability is less than 0.5, so the z-score must be negative, so
    we have to do an inverse look up for 1-0.2119=0.7881 then switch the sign
    of the corresponding z-score. The z-score giving a p-value of 0.7881 is 0.8,
    so the z-score we seek is -0.8.

    RonL
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