13.   A psychologist determined that the...

13.   A psychologist determined that thenumber of sessions required to obtain the trust of a new patient iseither 1,2, or 3. Let x be a random variable indicating thenumber of session required to gain the patients trust. Thefollowing probability function has been proposed.
     f(x) =x/6              for x = 1, 2, or 3


a. is this probability function valid? Explain
b. what is the probability that takes exactly 2 sessionsto gain the patients trust
c. what is the probability that it takes at least 2 sessionsto gain the patients trust
51. Of the 25 students (14 boys and 11 girls) in the 6thgrade class at St. Andrews school, 5 students were absentthursday.
a. what is the probability that 2 of the absent studentswere girls?
b.  what is the probability that 2 of theabsent students were boys?
c. what is the probability that all the absentstudents were boys?
d. what is the probability   that none of theabsent students were boys?

Answers ( 1 )

  1. maxime barnaby
    maxime barnaby
    We know that p(x)=1
                
                       p(x = (1/6)+(2/6)+(3/6) =1
         Therefore it is a valid probabilityfunction.
    prob.that takes exactly 2 sessions to gain thepatients trust is   p(x=2) =2/6
    prob.that it takes atleast 2 sessions to gain thepatients trust is p(x2)=(2/6)+(3/6)
       
    51. 5 absent students can be selected from 25 in ways
            2 absent girlstudents can be selected from 11 girls in ways
            3 absent boysstudents can be selected from 14 boys in ways
        probability that 2 of absentgirls is *
                                                            
                                                                       
       Similarly
       probability that 2 of the absentees were boysis     
                                                                                 
                                                                                              

       probability that all the absentees were boys is

    probability that none of the absent astudents were boys is

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