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Math Help - stats-percentage question

  1. #1
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    stats-percentage question

    kitchen appliances don't last forever. The lifespan of all microwave ovens sold in the united states is approximately normally distributed with a mean of 9 years and a standard deviation of 2.5 years. what percentage of the ovens last more than 10 years?

    a. 11.5%
    b. 34.5%
    c. 65.5%
    d. 69%
    e. 84.5%
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  2. #2
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    Re: stats-percentage question

    Standardise the data and find the value using the normal distribution table.

    \displaystyle P(X>X_0) = P\left( Z> \frac{X_0-\mu}{\sigma}\right)

    In your case

    \displaystyle P(X>10) = P\left( Z> \frac{10-9}{2.5}\right) = \cdots
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