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Show all your work. Indicate clearly the methods you use because you will be graded on the correctness of your methods as well as on the accuracy of your results and explanation.


A simple random sample of adults living in a suburb of a large city was selected. The age and annual income of each adult in the sample were recorded. The resulting data are summarized in the table below.


Annual Income

Age Category $25,000_$35,000 $35,001_$50,000 Over $50,000 Total

21_30 8 15 27 50

31_45 22 32 35 89

46_60 12 14 27 53

Over 60 5 3 7 15

Total 47 64 96 207


AWhat is the probability that a person chosen at random from those in this sample will be in the 31_45 age category? 89/207=0.43
BWhat is the probability that a person chosen at random from those in this sample whose incomes are over $50,000 will be in the 31_45 age category? Show your work.35/96=0.36
CBased on your answers to (a) and (b), is annual income independent of age category for those in this sample? Explain.

  1. The following table is the assignment of probabilities that describes the age (in years) and the gender of a randomly selected American student.

Age 14_17 18_24 25_34 +35

Male 0.01 0.30 0.12 0.04

Female 0.01 0.30 0.13 0.09


AWhat is the probability that the student is female? 0.53/100=0.0053
BWhat is the probability that the student is age 25_34? 0.25/100=0.0025
CWhat is the probability that the student is either male or at least 35 years old?
DWhat is the probability that the student is at least 35 years old? 0.04/0.47=0.085
EAre being a female and being at least 35 years old independent events? Provide statistical reasoning for your answer.

Verified Answer :

Q9: 
A) P(age group 31-45) =89/207   
                                     = 0.42995

B) P(age 31-45 I income over 50k)
                               = 35/96=0.36458

C) If annual income and age were independent, the probabilities in A) and B) would be equal. Since these probabilities are
not equal, annual income and age category are not independent
for adults in this sample.