A certain junior class has 1000 students and a certain senior class has 800 students. Among these students, there are 60 sibling pairs, each consisting of 1 junior and 1 senior. If 1 student is to be selected at random from each class, what is the probability that the 2 students will be a sibling pair?
a) 3/40000
b) 1/3600
c) 9/2000
d) 1/60
e) 1/15
Read the OE, didn't really get it? My answer was c) based on 60/1000 x 60/800... why not?
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OE was A)
Nevermind I got it... reason why it was 60/1000 x 1/800 was because of the wording.
The pair HAS to be the actual sibling pair, NOT just any 2 people in a sibling pair relationship. Thus it is 1/800 for the second ratio... !!
nevermind
Nevermind I got it... reason why it was 60/1000 x 1/800 was because of the wording.
The pair HAS to be the actual sibling pair, NOT just any 2 people in a sibling pair relationship. Thus it is 1/800 for the second ratio... !!
nevermind
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aimhigh715, dnt mind! I am not getting ur solution. According to the Qs, Among these students, there are 60 sibling pairs, each consisting of 1 junior and 1 senior.
So there will be 30 students of senior class and other 30 of junior class. If so, then how come you are getting 60/1000? Again why 1/800? I am getting confused here. I think we need some more input here.
So there will be 30 students of senior class and other 30 of junior class. If so, then how come you are getting 60/1000? Again why 1/800? I am getting confused here. I think we need some more input here.
Correct me If I am wrong
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Amitava
Regards,
Amitava
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Amitava, 60 pairs mean 60 sets of siblings (so 120 in total, 60 in junior class, 60 in senior class.)camitava wrote:aimhigh715, dnt mind! I am not getting ur solution. According to the Qs, Among these students, there are 60 sibling pairs, each consisting of 1 junior and 1 senior.
So there will be 30 students of senior class and other 30 of junior class. If so, then how come you are getting 60/1000? Again why 1/800? I am getting confused here. I think we need some more input here.
Now P(Getting a student from Junior who has a sibling in senior) = P(A) = 60/1000
Now since you have selected one student in the junior class, there will only be one student in senior class that will be his/her sibling...
P(B) = 1/800
P(A n B) = (60/1000).(1/800) = 60/800,000 = 3/400000