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 selected will be a sibling pair.
OA TO FOLLOW
A for sure.
The probability you can choose a junior who has siblings is 60/1000.
With a junior chosen, the probability you can choose his sibling in senior class is 1/800.
So the probability is 60/1000*1/800=3/40000 (It's so small!