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urgent question for probability!!

 
 
Reply Sun 28 Oct, 2012 11:08 am
From a group of 5 people (2 females, 3 males) a team of 3 needs to be picked. The selection is done randomly by picking names from a hat, one name at a time. The first person to be selected from the hat is the captain of the team. The next two people are the support members.
(i) What is the probability that the first name picked is a female?
(ii) What is the probability that the first name picked is a female if the second name picked is known to be female?
(iii) What is the probability that the captain is female if we know that at least one of the support members is also female?

my answer is
(i) p(F)= 0.4
(ii) P=P(F)*P(F|F)=0.4*0.25=0.1
(iii) P=0.4*0.25*1+0.4*0.75*(1/3)=0.2

I am afraid I misunderstand the last two questions ,,please do have a look at for me!!!many thanks!
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View best answer, chosen by jhxi1118
markr
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Reply Sun 28 Oct, 2012 12:34 pm
@jhxi1118,
Recall that Bayes' Theorem is:

P(A|B) = P(B|A)*P(A)/P(B)

i) P(A) = 2/5
ii) P(B|A) = 1/4, P(B) = 2/5
iii) P(B|A) = 1/2, P(B) = 7/10

Use P(A) from i to complete ii and iii.
jhxi1118
 
  1  
Reply Sun 28 Oct, 2012 01:35 pm
@markr,
many thanks!! I really mis understand the question!!
0 Replies
 
jhxi1118
 
  1  
Reply Fri 2 Nov, 2012 04:37 am
@markr,
hello. shall I asking, for question (ii), why the P(B) is 2/5 but not (2/5*1/4+3/5*2/4) ?thanks!!
engineer
 
  1  
Reply Fri 2 Nov, 2012 05:25 am
@jhxi1118,
2/5 = (2/5*1/4+3/5*2/4)
jhxi1118
 
  1  
Reply Sun 4 Nov, 2012 07:31 am
@engineer,
haha..sorry my fault...thanks
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