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    asiunia66 Posts: 1, Reputation: 1
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    Nov 27, 2009, 05:14 AM
    Statistics normal disribution
    The longevity of people living in certain locality has a standard deviation of 14 years. What is the mean longevity if 30% of the people live longer than 75 years? Assume a normal distribution for life spans.
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    galactus Posts: 2,271, Reputation: 282
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    Nov 27, 2009, 10:54 AM
    Quote Originally Posted by asiunia66 View Post
    The longevity of people living in certain locality has a standard deviation of 14 years. What is the mean longevity if 30% of the people live longer than 75 years? Assume a normal distribution for life spans.

    If 30% live longer than 75 years, then 70% live 75 years or less.

    Since the normal distribution moves left to right, we want the area in the upper 30% shaded. Look up the z-score for .7

    Then, use

    and solve for
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