概率题目请指教，谢谢。

The passing rate for a license exam is 87%, what is the probability that a person will not pass it until his or her second or third attempt?

所有跟帖： 

• 0.127803 -jinjing- ♀ (38 bytes) () 05/11/2016 postreply 10:50:34

• 非常感谢。　可否稍微解释一下？　 -pittsburgh- ♀ (23 bytes) () 05/21/2016 postreply 05:41:22

• 试详答. -jinjing- ♀ (376 bytes) () 05/22/2016 postreply 07:28:38