Question

A challenge to all OpenStudiers! (difficulty: normal)
In an entrance test, there are multiple choice questions. There are four possible answers to each question of which exactly one option is correct. The probability that a student knows the answer to a question is 90%. If he doesn't know the answer, he guesses randomly. Given that he gets the correct answer to a question, what's the probability that he guessed it? (Time limit: atmost 5 mins)

Answer 1

Well, if he guessed it, there's only a 10% chance since there's a 90% chance that a student knows the answer to a question.

Answer 2

At least from my interpretation.

Answer 3

chance and probability are different!

Answer 4

probability =\[probability = \frac{ number of favorable outcomes }{ numberofequally likely outcomes }\]

Answer 5

there are 2 outcomes! he either guessed it or didnt guess it right? so its 50/50?

Answer 6

dunno. i made this all up as i went along. -_-

Answer 7

?

Answer 8

Any more answer guys?

Answer 9

please do not let other people do your homework, yttrium

Answer 10

this is a trivial conditional probability problem

Answer 11

ooh i guess since it is a guess, the fact that there are 4 choices to guess from also matters!

Answer 12

lol i know the solution and its not a homework

Answer 13

2.5% would be my only other guess. i have never taken stat before!

Answer 14

$50 US dollars deposit into my account, for me to give the correct answer and solution

Answer 15

amazon gift card of the same value works also

Answer 16

I'll donate 90% of the amount to open study

Answer 17

what is the probability that he is lying?