A certain junior class has 1000 students and a certain senior class has 800 students. Among these students, there are 60 siblings 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 selected will be a sibling pair?
A. 3/40000
B. 1/3600
C. 9/2000
D. 1/60
E. 1/15
OA A
Source: GMAT Prep
A certain junior class has 1000 students and a certain
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There are 60 sibling pairs.BTGmoderatorDC wrote:A certain junior class has 1000 students and a certain senior class has 800 students. Among these students, there are 60 siblings 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 selected will be a sibling pair?
A. 3/40000
B. 1/3600
C. 9/2000
D. 1/60
E. 1/15
OA A
Source: GMAT Prep
The probability of selecting a sibling from the junior class is 60/1,000.
The probability of selecting the other member of the sibling pair from the senior class is 1/800.
The probability that both students selected will be a sibling pair is 60/1,000 * 1/800 = 3/40,000.
The correct answer is choice A.
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The probability of selecting any one sibling from the 60 sibling pairs in the junior class is 60/1000. Once that person is selected, the probability of selecting his or her sibling from the senior class is 1/800; thus, the probability of a selecting a sibling pair is:BTGmoderatorDC wrote:A certain junior class has 1000 students and a certain senior class has 800 students. Among these students, there are 60 siblings 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 selected will be a sibling pair?
A. 3/40000
B. 1/3600
C. 9/2000
D. 1/60
E. 1/15
60/1000 x 1/800 = 3/50 x 1/800 = 3/40000
Alternatively, the probability of selecting any one sibling from the 60 sibling pairs in the senior class is 60/800. Once that person is selected, the probability of selecting his or her sibling from the junior class is 1/1000; thus, the probability of a selecting a sibling pair is:
60/800 x 1/1000 = 3/40 x 1/1000 = 3/40000
Answer: A
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Probability = number of ways to select 1 junior and 1 senior such that they make a sibling pair / number of ways to select 1 junior and 1 senior.
= 60 / (1000*800)
= 60 / 800000
= 3 / 400000
Or option A. Regards!
= 60 / (1000*800)
= 60 / 800000
= 3 / 400000
Or option A. Regards!