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~

(60/1000)*(1/800)

第一个选出来之后，第二个就只有一种选择了，是不是错这儿了。