The Total solution for NCERT class 6-12
Let E1 bethe event that the student knows the answer, E2 be the eventthat the student guess the answer and A be the event that the answer iscorrect.
Then P (E1)= ¾
And P (E2)= ¼
Also P (A|E1)= P (correct answer given that he knows) = 1
And P (A|E2)= P (correct answer given that he guesses) = ¼
Now the probabilitythat he knows the answer, being given that answer is correct, is P (E1|A).
By using Bayes’theorem, we have: