Crystal Computer Company
Expected Value and Standard Deviation of Random Variables
Worksheet 12
 

Crystal Computer Company is considering using extra space in its retail store to introduce a new video product. Based on customer behavior toward other new products, Crystal calculates the expected value of daily profit from sales of the new product to be $200. However, Crystal must also hire a consultant to install and service the new product as part of the package customers receive. This consultant will work any number of hours per day at $40 per hour (this value includes fringe benefits). These wages would be the only additional cost to Crystal. Assume that the availability of the consultant is independent of sales (it does not affect the probability distribution of sales).

a.     How many hours should this salesperson average per day, if Crystal wants to
        avoid losing money while having the consultant available as many hours per day
        as possible?    Explain your answer.

b.     If the standard deviation of the daily profit random variable is $40, how many
        daily hours should the sales person average so that Crystal is almost certain to
        not lose money?    Explain using the Empirical rule. What assumption must you
        make to do this?

c.     If the standard deviation of the daily profit random variable is $20, how many
        daily hours should the sales person average so that Crystal is almost certain to
        not lose money?    Explain using the Empirical rule.

d.     Is the assumption of independence of consultant availability and sales
        reasonable?     Explain.
 
 

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Useful Excel Random Variable Functions
 

1.    @STANDARDIZE(x, m, s) = (x-m)/s

2.    @BINOMDIST(x, n, p, FALSE) = P(X=x)        TRUE = 1     and     FALSE = 0

       @BINOMDIST(x, n, p, TRUE) = P(X  <  x)

3.    @NORMSDIST(z)The S between NORM and DIST is for STANDARD.

       @NORMSINV(p)

4.    @NORMDIST(x, m, s, TRUE) = P(X  <  x)

       @NORMDIST(x, m, s, FALSE) = f(x)

5.    @NORMINV(p, m, s)
 
 

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