回複：If you are right,it shoul be from real data.P(b)=13/27

I believe this is the ‘expected’ answer to this question. You can always argue that the question was not soundly stated though (though actually it is generally soundly stated).

13/27 is a right answer

1/3 could be a right answer…

½ could be a right answer …

要真正完全理解這道題，

1- 應明白這三個答案的來龍去脈
2- 你應可以擴展或改寫題目，create a scenario/story/question that make 1/3 and ½ correct.