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Math Help - [SOLVED] Normal Distrubtion Question

  1. #1
    Member looi76's Avatar
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    [SOLVED] Normal Distrubtion Question

    Question:
    Given that X \sim N(44,25), find t correct to 2 decimal places when
    P(X \geq t)=0.7704

    Attempt:

    = P(X \geq t)=0.7704

    \mu = 44 , \sigma^2 = 25 , \sigma= 5

    = P(\frac{X-\mu }{ \sigma } \geq \frac{X-44}{ 5})

    1 - \frac{X-44}{5} = 0.7704

    1 - 0.7704 = \frac{X-44}{5}

    0.26 = \frac{X-44}{5}

    1.3 = X - 44

    X = 45.3

    Where did I go wrong?
    Last edited by looi76; April 16th 2008 at 04:46 AM.
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  2. #2
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    Quote Originally Posted by looi76 View Post
    Question:
    Given that X \sim N(44,25), find s, t, u, and v correct to 2 decimal places when
    P(X \geq t)=0.7704

    Attempt:
    = P(\frac{X-\mu }{ \sigma } \geq \frac{X-44}{ 5})

    1 - \frac{X-44}{5} = 0.7704
    This is the problem here. You need to use a normal probability table to find that
    \Pr(Z \geq -0.74) = 0.7704

    Then we have:
    <br />
 -0.74 = \frac{t-44}{5}<br />
\Rightarrow t = 40.3
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