第一个不是100吗?!要是第一个是100答案是1/50
=(99/100)*(98/99)*(97/98)*.*(3/4)*(2/3)
=2/100
=1/50
第一个是1000
=(999/1000)*(98/99)*(97/98)*.*(3/4)*(2/3)
=999/1000*2/99
= 111/5500
第一个不是100吗?!要是第一个是100答案是1/50
=(99/100)*(98/99)*(97/98)*.*(3/4)*(2/3)
=2/100
=1/50
第一个是1000
=(999/1000)*(98/99)*(97/98)*.*(3/4)*(2/3)
=999/1000*2/99
= 111/5500