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					                                                    Name:
                                                    Student #:


                                   DCAD 7350 3.0
                                         Test
                                   (October 24, 2008)

Time allowed: 180 minutes
Aids permitted: Calculator(s), One 2-sided 8.5”x11” formula sheet

Instructions:

 1. Check that you have all 9 pages (including this cover page) of the test.

 2. Answer the questions in the spaces provided. If you need more space, be sure to
    indicate clearly where the rest of your answer can be found.

 3. Marks for each question are as indicated. You should allocate your time accordingly.

 4. Your work must justify the answer you give.



                               ∼ GOOD LUCK ∼


                           FOR INSTRUCTOR’S USE ONLY


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Question 1: (10 marks) A new filter system for swimming pools is designed to filter out
certain harmful particles that can get into the water. A study shows that the number of
particles per gallon of water is normally distributed with a mean of 20000 and a standard
deviation of 3000. The filter is designed to catch 25000 particles per gallon.

 a. (5 marks) Determine the probability that the filter will allow some particles to escape
    back into the pool.




 b. (5 marks) The manufacturer of the filter claims that the filter removes 90% of the
    particles from the water. How many particles per gallon of water would the filter
    remove?
Question 2: (10 marks) Rolling Hills is a semiprivate golf club in rural North Carolina.
Like most golf courses, Rolling Hills constantly battle the slow-play issue. The manager
timed 45 players playing an 18-hole round. Let x be the time (in minutes) it took these
45 players to complete the round. The manager reported the data histogram is roughly
symmetrical with n xi = 11774 and n (xi − x)2 = 19292. Moreover the fastest and the
                     i=1                 i=1     ¯
slowest players to complete the round took 231 minutes, and 345 minutes respectively.

 a. (3 marks) Calculate the mean time it took these 45 players to complete the round.
    Also report the standard deviation.




 b. (4 marks) Check if the fastest and the slowest players are outliers?




 c. (3 marks) The upper quartile of this data set is 267 minutes. How many standard
    deviation it is away from the mean?
Question 3: (10 marks) The Slimy Soap Company has two production facilities, one in
Ontario and one in Alberta. The Ontario plant makes 60% of the company’s total soap
output, and the Alberta plant makes the rest of it. The quality assurance manager deter-
mined that 5% of the soap produced in Ontario and 10% of the soap produced in Alberta is
unusable due to some quality problems.

 a. (5 marks) If a bar of soap is randomly selected from the display in Loblaws, what is
    the chance that the soap is unusable?




 b. (5 marks) If a bar of soap is randomly selected from the display in Loblaws and is
    known to be unusable, what is the probability that it was produced by the Ontario
    plant?
Question 4: (10 marks) The personnel manager of the Cumberland Pig Iron Company is
studying the number of on-the-job accidents over a period of one month. He developed the
following probability distribution.

                  Number of Accidents      0    1     2    3   4
                  Probability             0.40 0.20 0.20 0.10 0.10

 a. (4 marks) Compute the mean, and standard deviation of the number of accidents in a
    month.




 b. (3 marks) Let Xi be the number of on-the-job accidents in the i-th month. Assume
    Xi and Xj are independent random variables for all i = j. Furthermore let T be the
    total number of on-the-job accidents over a 12 months period (i.e. T = X1 + · · · X12 ).
    What is the mean and standard deviation of T ?




 c. (3 marks) Continue from part (b), What is the mean and variance for T /12, which is
    the average number of on-the-job accidents.
Question 5: (10 marks) Information from the American Institute of Insurance indicates
the amount of life insurance per household in US is normally distributed with mean $100000
and standard deviation of $40000.

 a. (2 marks) A household is randomly selected. What is the probability that the life
    insurance policy for this household is exactly $100000?




 b. (4 marks) A random sample of 25 households are randomly selected. What is the
    probability that the average life insurance policy for these household is at least $112000?




 c. (4 marks) What is the average life insurance policy of 25 household such that it will
    be exceeded by 2.5% of all the life insurance policy?
Question 6: (10 marks) The manager of the grocery store, Dawdle, collected information
on the waiting time at the checkout counter. Part of his result is reported in the following
stem-and-leaf plot where the leaf unit is 0.1 minutes.

5      1
5      5
6      44
6      677
7      1344
7      56778
8      022344
8      5667789
9      01123
9      57

    a. (1 marks) Comment on the overall shape of the given plot.




    b. (5 marks) Calculate the 5-number summary.




    c. (4 marks) Identify all the outliers (if exists).
Question 7: (10 marks) The Wood County sheriff classifies crimes by age (in years) of
the criminal and whether the crime is violent or nonviolent. As shown below, a total of 150
crimes were reported by the sheriff last year.

                                             Age (in years)
                      Type of Crime    Uner 20 20 to 40 Over 40
                      Violent            27        41       14
                      Non violent        12        34       22

 a. (3 marks) A case from last year is randomly selected. What is the probability that the
    selected case involved a violent crime or an offender less than 20 years old?




 b. (3 marks) A case from last year is randomly selected. It is reported that the case
    involved a violent crime. What is the probability that the crime was committed by a
    person under 20 years old?




 c. (4 marks) Two cases are randomly selected. What is the probability that exactly one
    involved a violent crime?
Question 8: (10 marks) Past sales records indicate that sales at the store are skewed with
a long right tail. Assume the population mean sales is $12.50 per customer with a standard
deviation of $5.50. The store manager has selected a random sample of 100 sales receipts.

 a. (5 marks) What is the probability that the mean sales is between $12.25 and $13.00?




 b. (5 marks) What is the probability that the mean sales exceed $14.00? Is it a rare
    event? Why?

				
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