A certain junior class has 1,000 students and a certain senior class has 800 students. Among these students, there are 20 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 at will be a sibling pair? Choose the correct choice from the following options: A) 3/40,000 B) 1/3,600 C) 9/2,000 D) 1/40,000 E) 1/15
Total number of ways of choosing one student from each group is = 800 * 1000   Number of cases in which a sibling pair will be got is = 60   Thus the probability that the 2 students selected will be a sibling pair is   = 20 /(800 * 1000)   = 1/40,000   1/40,000
<result>D</result>
A certain junior class has 1,000 students and a certain senior class has 800 students. Among these students, there are 20 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 at will be a sibling pair?