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Math Help - Standard deviation problem

  1. #1
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    Standard deviation problem

    A little homework help please =/ ... Thank you in advance


    The average starting salary for this year's graduates at a large university is $20,000 with a standarad deviation of $8,000. Furthermore, it is known that the starting salaries are normally ditributed.

    a. What is the probability that a randomly selected LU graduate will have a starting salary of at least 30,400?


    b. Individuals with starting salaries of less than $15,600 receive a low income tax break. What percentage of the graduate will receive tax break?

    c. What are the minimum and the maximum starting salaries of the middle 95% of the LU graduates?

    d. If 189 of the recent graduates have salaries of at least $32,240, how many students graduate this year from the university?
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  2. #2
    MHF Contributor matheagle's Avatar
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    I'll do the first one

    P( X> 30,400)=P\biggl( {X-20,000\over 8000}> {30,400-20,000\over 8000}\biggr)=P(Z>1.3)\approx .0968.

    The next one is P( X< 15,600)...
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