有一道数学题，前两遍看都做出来的是正确答案，今天又看，心理很纠结，各位帮忙看看，谢谢啦
OG
A certain junior class has 1000 students and a certain senior calss 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 calss,what is the probality that the 2 students selected will be a sibling pair?
答案：3/40000
为什么不是9/2000?
谢谢啊~ | 
