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# In an entrance test there are multiple choice questions. There are four possible answers to each question, of which one is corret.The probability that a student know the answer to a question is 9/10.If he gets the correct answer to a question, then the probability that he was guessing is(post ur ans in Step by step understandable way) Grade:12th Pass

## 1 Answers

7 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.

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