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Math Help - Please Help 1

  1. #1
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    Please Help 1

    1. Assume blood pressure readings are normally distributed with a mean of 120 and standard deviation of 8. What percentage of people have a blood pressure reading greater than 145?

    2. Assume that the salaries of elementary school teachers in the United States are normally distributed with a mean of $41,000 and a standard deviation of $4,000. What is the cut-off salary for teachers in the bottom 10%?


    I greatly appreciate any one's help. These are problems I have struggled with this semester....and now that the end is winding down I would love to figure them out for future references. Thank so much to everyone!
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  2. #2
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    Quote Originally Posted by loutja35 View Post
    1. Assume blood pressure readings are normally distributed with a mean of 120 and standard deviation of 8. What percentage of people have a blood pressure reading greater than 145?

    2. Assume that the salaries of elementary school teachers in the United States are normally distributed with a mean of $41,000 and a standard deviation of $4,000. What is the cut-off salary for teachers in the bottom 10%?


    I greatly appreciate any one's help. These are problems I have struggled with this semester....and now that the end is winding down I would love to figure them out for future references. Thank so much to everyone!
    1. \Pr(X > 145) = \Pr\left(Z > \frac{25}{8} \right) = 1 - \Pr\left(Z < \frac{25}{8} \right). The value of Z is found from Z = \frac{X - \mu}{\sigma}. You should have been taught how to calculate probabilities from a standard normal distribution.

    2. Calculate the value of z* such that \Pr(Z < z^*) = 0.1. Then the cut-off salary, x*, is found from z^* = \frac{x^* - 41,000}{4,000}.

    Note that z* is negative.
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  3. #3
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    Quote Originally Posted by loutja35 View Post
    1. Assume blood pressure readings are normally distributed with a mean of 120 and standard deviation of 8. What percentage of people have a blood pressure reading greater than 145?
    HI

     X - N (120 , 8^2)

    P(X>145)=P(Z>\frac{145-120}{8})

    calculate this using the tables or calculator to get the probability , then convert it to percentage .
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