回复：回复：5/36

1/2*1/2 --- for odd numbers
1/9 ---- for 9 which is not prime number

1/4-1/9=5/36

所有跟帖： 

• 回复：回复：回复：5/36 -Jinjing- ♀ (78 bytes) () 02/07/2010 postreply 07:52:16

• You are right! -pj- ♂ (0 bytes) () 02/08/2010 postreply 14:08:47

• 回复：回复：回复：5/36 -wxczcbm- ♂ (160 bytes) () 02/07/2010 postreply 22:20:10

• 回复：回复：回复：回复：5/36 -greenfarm- ♀ (0 bytes) () 02/08/2010 postreply 10:13:27

• you are right. possibility for odd number is wrong -pj- ♂ (27 bytes) () 02/08/2010 postreply 14:09:53