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Math Help - A probability question and an Expectations question

  1. #1
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    A probability question and an Expectations question

    Two questions I need some help with,

    First question. This has something to do with expectations and its properties.

    The sales per day for a product is estimated as follows based on past records

    Daily demand (X) / Probaility

    10 / .1
    11 / .2
    12 / .4
    13 / .3

    a. Obtain the mean and variance of the daily sales.
    b. If the porfit can be described by the equation, profit= -10+(4*X)

    What is the expected daily profit? What is the variance of the daily profit?



    2. An insurance company runs three offices, A, B and C. The company's employess are distirbuted as follows; 30% work in office A, 20% in Off. B and 505 in Off. C.
    In office A 10% are managers, in office B 20% are managers and in office C 5% are managers

    a. What is the total proportion of managers in the company?
    b. If a member of staff, randomly chosen, turns out to be a manager, what is the probability that she works in office A.

    My answer for part a is 0.095 or 9.5%. I' not sure on part b though, I think it has something to do with conditional probability.
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  2. #2
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    In the first problem, you need to recoqnize that you have been given a frequency function for sales. Once you do that, apply the usual formula for the mean of a random variable given a frequency function.
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