Answer Choices: (A) 3/40,000 (B) 3/20,000 (C) 3/4,000 (D) 9/400 (E) 6/130 Source - VeritasPrep Practice Test Answer Choices: (A) 3/40,000 (B) 1/3,600 (C) 9/2,000 (D) 1/60 (E) 1/15 Source - GMATPrep Practice Test OA - Soon PS: Please click on the image to view the complete question.

Basic principle of both the question is same. (Incidentally the answer is same too! ) I'll explain the first one. Number of possible ways to select two students such that one of them is a junior student and another is a senior student = (Number of possible ways to select a junior student out of 1000)*(Number of possible ways to select a senior student out of 800) = 1000*800 Number of possible ways to select a sibling pair = (Number of possible ways to select one of them out of 60)*(Number of possible ways to select other one of them out of 60) = 60*1 (Number of possible ways to select other one of them out of 60 is 1 because as the first one is already selected other one is fixed for him/her.) Therefore required probability = 60/(800*1000) = 3/40,000 The correct answer is A.

Rahul@gurome wrote:Basic principle of both the question is same. (Incidentally the answer is same too! ) I'll explain the first one. Number of possible ways to select two students such that one of them is a junior student and another is a senior student = (Number of possible ways to select a junior student out of 1000)*(Number of possible ways to select a senior student out of 800) = 1000*800 Number of possible ways to select a sibling pair = (Number of possible ways to select one of them out of 60)*(Number of possible ways to select other one of them out of 60) = 60*1 (Number of possible ways to select other one of them out of 60 is 1 because as the first one is already selected other one is fixed for him/her.) Therefore required probability = 60/(800*1000) = 3/40,000 The correct answer is A. Thanks for the explanation Rahul. But dont i need to take into consideration the way/sequence in which i select the siblings?? i.e in one sequence- i first select a sibling form Junior class and then select the matching one from senior class. and in the 2nd sequence- i first select a sibling form senior class and then select the matching one from junior class