pratiksha agarwal
Last Activity: 11 Years ago
E1=he guesses the answer
E2=he knows the answer
given P(E2)=9/10
as they are mutually exclusive then P(E1)+P(E2)=1
so P(E1)=1/10
A=he answers correctly
P(A/E1)=he guesses and answers correctly=1/4
as there are 4 options and only one can be correct by guessing
P(A/E2)=he gives correct answer as he knows the answer=1
if one knows the answer he will obviously give correct answer
now using baye''s theorem
P(E1/A)=we know answer is correct and we have to take out probability that he guessed and gave correct answer=
P(E1)*P(A/E1)/(P(E1)*P(A/E1)+P(E2)*P(A/E2))
putting values one can find answer.