In the new pattern of IIT-JEE paper there are multiple choice questions. There are 4 possible answers to each question of which one is correct. The probability that a student knows the answer to a question is 90% . If he gets the correct answer to a question then the probability that he was guessing is

see full answer

Start JEE / NEET / Foundation preparation at rupees 99/day !!

21% of IItians & 23% of AIIMS delhi doctors are from Sri Chaitanya institute !!

An Intiative by Sri Chaitanya

$\frac{1}{37}$

$\frac{4}{37}$

$\frac{1}{4}$

$\frac{37}{40}$

answer is A.

(Unlock A.I Detailed Solution for FREE)

Ready to Test Your Skills?

Check your Performance Today with our Free Mock Test used by Toppers!

Take Free Test

Detailed Solution

$A_{1}$ : He knows the answer
$A_{2}$ : He guess the answer
E : He gets the correct answer
$P (A_{1}) = \frac{9}{10}, P (A_{2}) = 1 - \frac{9}{10} = \frac{1}{10}, P (\frac{E}{A_{1}}) = 1, P (\frac{E}{A_{2}}) = \frac{1}{4}$
∴ required probability=P( he was guessing /he gets the correct answer)

$P (\frac{A_{2}}{E}) = \frac{P (A_{2}) P (\frac{E}{A_{2}})}{P (A_{1}) P (\frac{E}{A_{1}}) + P (A_{2}) P (\frac{E}{A_{2}})}$
$= \frac{\frac{1}{10} \cdot \frac{1}{4}}{\frac{9}{10} \cdot 1 + \frac{1}{10} \cdot \frac{1}{4}} = \frac{1}{36 + 1} = \frac{1}{37}$

Watch 3-min video & get full concept clarity

Result Producing online coaching for JEE/NEET of south India

Largest All India Test Series for JEE/NEET

Best Books for IIT JEE

Best Books for NEET

How to Join IIT after 10th

Get Expert Academic Guidance – Connect with a Counselor Today!

Result Producing online coaching for JEE/NEET of south India

Largest All India Test Series for JEE/NEET

Best Books for IIT JEE

Best Books for NEET

How to Join IIT after 10th