Q82 / 125 · BITSAT 2018 · Mathematics
In a test an examiner either guesses or copies or knows the answer to a multiple choice question with choices. The probability that he/she makes a guess is . The probability that he/she copies the answer is . If the probability that the answer is correct, given that he/she copied it is , then the probability that he/she knows the answer to a question given that he/she correctly answered it, is
- A
- B
- C
- Correct answerD
Solution
Let be the event that the examinee gives the correct answer.
Let stand for guessing, copying and knowing. respectively.
Given,
and
Also, for if the examinee knows, he/she will correctly answer it and
since there are four choices.
Now, total probability
Now,
Hence, the correct answer is option: 'D'.