One step further

来源: 于 2014-09-30 11:51:04 [博客] [旧帖] [给我悄悄话] 本文已被阅读：次
We can further divide case B into B2 and B3, where B2 is the door opened by host, and B3 is the third one.

P_B2 = 0 (host will only open door with Goat), Therefore,

P_B3 = P_B - P_B2 = 2/3 - 0 = 2 / 3