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Homework answers / question archive / 1)The shape of any uniform probability distribution is           A)  Negatively skewed       B)  Positively skewed       C)  Rectangular       D)  Bell shaped   2

1)The shape of any uniform probability distribution is           A)  Negatively skewed       B)  Positively skewed       C)  Rectangular       D)  Bell shaped   2

Economics

1)The shape of any uniform probability distribution is

 

 

      A)  Negatively skewed

      B)  Positively skewed

      C)  Rectangular

      D)  Bell shaped

 

2.   Suppose that in a certain part of the world in any 50-year period the probability of a major plague is 0.39, the probability of a major famine is 0.52 and the probability of both a plague and a famine is 0.15.  What is the probability of a famine given that there is a plague.

      A) 0.24

      B) 0.288

      C) 0.370

      D) 0.385

 

3.    A new drug has been developed that is found to relieve nasal congestion in 90 percent of those with the condition.  The new drug is administered to 300 patients with the condition.  What is the probability that more than 265 will be relieved of nasal congestion?

      A)  0.0916

      B)  0.1922

      C)  0.8078

       D) 0.3078

 

 

4.  Each new employee is given an identification number.  The personnel files are arranged sequentially starting with employee number 0001.  to sample the employees, the number 0153 was first selected then numbers 0253, 0353, 0453 and so on became members of this sample.  This type of sampling is called:

      A) Simple random sampling

      B) Systematic sampling

      C) Stratified random sampling

      D) Cluster sampling

 

5.   The mean amount spent by a family of four on food per month is $500 with a standard deviation of $75.  Assuming that the food costs are normally distributed, what is the probability that a family spends less than $410 per month?

      A)  0.2158

      B)  0.8750

      C)  0.0362

      D)  0.1151

 

 6.  Which of the following is NOT true regarding the normal distribution?

            A)  Mean, median and mode are all equal

            B)   It has a single peak

            C)   It is symmetrical

            D)  The points of the curve meet the X-axis at z = –3 and z = 3

 

7.   What is the area (percentage) under the normal curve between z = 0.0 and z = 2.0?

            A)  1.0000

            B)   0.7408

            C)   0.1359

            D)  0.4772

 

 

8.    Companies proved to have violated pollution laws are being fined various amounts with the following probabilities.

      Fines (QR)            1000                10000              50000              100000

      Probability               0.4                   0.3                   0.2                   0.1

     

      What are the mean and standard deviation for the fine variable?

ANS: C

              

 

 

9.  The mean score of a college entrance test is 500; the standard deviation is 75.  The scores are normally distributed.  What percent of the students scored below 320?

            A)  About 50.82%

            B)   About 34.13%

            C)   About 7.86%

            D)  About 0.82%

 

10.     In a 1974 “Dear Abby” letter a woman lamented that she had just given birth to her eighth child and all were girls!  Her doctor assured her that the chance of the eighth child being a girl was only 1 in 100.  What was the real probability that the eighth child would be a girl?

         A) 0.5

         B) 0.0039

         C) 0.01

         D) 0

 

 

11.    A large manufacturing firm tests job applicants who recently graduated from college. The test scores are normally distributed with a mean of 500 and a standard deviation of 50.  Management is considering placing a new hire in an upper level management position if the person scores in the upper 6 percent of the distribution.  What is the lowest score a college graduate must earn to qualify for a responsible position?

            A)  50

            B)   625

            C)   460

            D)  578

 

 

12.  Two normal distributions are compared.  One has a mean of 10 and a standard deviation of 10.  The second normal distribution has a mean of 10 and a standard deviation of 2.  Which of the following it true?

            A)  the locations of the distributions are different

            B)   the distributions are from two different families

            C)   the dispersions of the distributions are different

            D)  the dispersions of the distributions are the same

 

 

 

13.

 

 

Given the distribution of a discrete random variable X as shown below, the expectation      of X, E(X), is

 

x

P (X = x)

0

0.15

1

0.20

2

0.35

3

0.30

 

            A)  0.15     B.  1.80     C.   0.90      D.  1.

 

 

 

 

 

 

14.  A group of statistics students decided to conduct a survey at their university to find the average (mean) amount of time students spend studying per week.  Based on a simple random sample, they surveyed 144 students.  The statistics showed that students studied an average of 20 hours per week with a standard deviation of 10 hours.

 

 

                        a) What is the standard error of the mean?

                                    A)        0.83

                                    B)        10

                                    C)        0.5

                                    D)        2

 

                        b) What is the probability that a sample mean would exceed 20 hours per week?

                                    A)        1.0

                                    B)        0.5

                                    C)        1.96

                                    D)        Cannot be calculated based on the given information.

 

                        c) What is the probability of finding a sample mean less than 18 hours?

                                    A)        0.4820

                                    B)        0.4920

                                    C)        0.0080

                                    D)        0.0180

 

                  d) What is the probability that average student study time is between 18 and 22  hours?

                                    A)        0.9640

                                    B)        0.0160

                                    C)        0.0360

                                    D)        0.9840

 

 

 

 15.         If  and  , what is ?

 

                       a) 28                 b)  35               c)  840             d) 2401

 

 

 

16.     A sales representative calls on four hospitals in Westchester County.  It is immaterial        what order he calls on them.  How many ways can he organize his calls?

                        A)        4

                        B)        24

                        C)        120

                        D)        37

 

17.  There are 10 rolls of film in a box and 3 are defective.  Two rolls are to be selected, one after the other.  What is the probability of selecting a defective roll followed by another defective roll?

                        A)  1/2, or 0.50

                        B)  1/4, or 0.25

                        C)  1/120, or about 0.0083

                        D)  1/15, or about 0.07  

 

 

18.   The mean score on a college placement exam is 500 with a standard deviation of 100.  Ninety-five percent of the test takers score above what?

                        A)        260

                        B)        336

                        C)        405

                        D)        664

 

 

 

19.   A soft-drink company produces a drink called Super-Drink. They advertise 355 ml on the can. The filling process follows a normal distribution with a mean value of  = 357 ml with a standard deviation of  = 1.5 ml . What is the probability that a randomly chosen drink is under-filled (that is has less than the amount advertised on the can)?

  a)         9.1 %             

                    b)         9.5 %

                    c)          9.8 %

                    d)         10.6 %

 

 

 

20.  The first card selected from a standard 52-card deck was a king. If it is returned to the deck, what is the probability that a king will be drawn on the second selection?

                  A)  1/4 or 0.25

                  B)  1/13, or 0.077

                  C)  12/13, or 0.923

                  D)  1/3 or 0.33

 

 

 

 21.The first card selected from a standard 52-card deck was a king. If it is NOT returned to the deck, what is the probability that a king will be drawn on the second selection?

                  A)  1/3 or 0.33

                  B)  1/51, or 0.0196

                  C)  3/51, or 0.0588

                  D)  1/13 or 0.077

 

 

 

22.       The mean score of a college entrance test is 600; the standard deviation is 80. The scores are normally distributed. 

 

            a) Label the normal curve                                                                        

           

           

            b) What score is the 70th percentile?                                                        

           

            c)  What percent of the students fell between 600 and 800?                  

 

 

 

 

 

23. David's gasoline station offers 4 cents off per gallon if the customer pays in cash and does not use a credit card.  Past evidence indicates that 40% of all customers pay in cash.  During a one-hour period twenty-five customers buy gasoline at this station.

 

 

            a)         What is the probability that at least ten pay in cash? [2]

           

                                        

             

             

            b)         What is the probability that no more than twenty pay in cash? [2]

             

                                   

             

c)         What is the probability that more than ten and less than fifteen customers pay in cash? [2]

             

             

 

 

24. A company is studying the number of monthly absences among its 125 employees.  The following probability distribution shows the likelihood that people were absent 0, 1, 2, 3, 4, or 5 days last month.

 

 

a)  What is the mean number of days absent?

 

 

b)   What is the standard deviation?

 

 

       c)  Given the probability distribution, which of the following predictions is correct?

            A)  60% of the employees will have more than one day absent for a month

            B)   There is a 0.04 probability that an employee will be absent 1 day during a month

            C)   There is a 0.12 probability that an employee will be absent 2 days during a month

            D)  There is a 0.50 probability that an employee will be absent 0.72 days during a month.

 

 

 

 

25.       A large manufacturing firm tests job applicants who recently graduated from college. The test scores are normally distributed with a mean of 500 and a standard deviation of 50.  Management is considering placing a new hire in an upper level management position if the person scores in the upper 6 percent of the distribution.  What is the lowest score a college graduate must earn to qualify for a responsible position?

 

 

 

 

 

 

26.       A survey found that the American family generates an average of 17.2 pounds of glass garbage each year.  Assume the standard deviation of the distribution is 2.5 pounds.  Find the probability that the mean of the sample of 55 families will be between 17 and 18 pounds. [3]

 

 

 

 

27.  A grocery store manager notes that 35% of customers who buy a particular product make use of a store coupon to receive a discount.  Four people purchase the product.

     

      a)  Identify the success probability, p.                                               

 

 

      b) Develop a probability distribution showing probabilities

for the four customers using a coupon

 

X

P(X)

0

0.179

1

0.384

2

0.311

3

0.111

4

0.015

                                                                                                                                                                                                                       

      c)  What is the probability that more than 2 customers used a coupon?                                                                                                                                                                                                                                                        

 

 

 

e)  What is the expected number of customers using a coupon?       

 

 

 

                        f)  What is the standard deviation for this problem?                         

 

                       

 

 

 

 

 

 

             

28.      The coach of a track team can send only the top 5% of her runners to a regional track meet.  For the members of her team, times for a 1-km run are normally distributed with a mean of 5.6 min and a standard deviation of 0.76 min.  Be careful, the faster the runner the better!

a)  Label the curve                       

 

 

b)       What is the cut-off time to determine which members of the team qualify for the regional meet?                                                                                         

 

 

 

 

 

c)        Her junior team consists of 20 runners what is the probability that the mean of this time will be less than 5.5 minutes?                                                 

 

 

 

30.    Every day Morse attempts the crossword puzzle in his newspaper. The time taken, X minutes, to complete the crossword may be modeled by a Normal Distribution with mean 22 minutes and standard deviation 4.5 minutes.

 

    1. Calculate the probabilities that he takes

 

i)         less than 25 minutes to complete the crossword

 

 

 

ii)        more that 15 minutes to complete the crossword.                                                

 

 

iii)      between 15 and 25 minutes to complete the crossword.

 

 

    1. What length of time would be enough for Morse to finish the crossword on 95% of days?                                         

 

 

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