With respect to a particular question on a multiple choice test (having 4 alternatives with only 1 correct) a student knows and therefore can elimlnate 3 of the 4 choices from consideration with probability 2/3 , can eliminate 2 of the 4 choices from consideration wid probability 1/6, can eliminate 1 choice from consideration wirh probability 1/9 and can eliminate none with probability 1/18 . If the student knows the answer , he answers correctly otherwise he guesses from among the choices not eliminated.If the answer given by the student was found correct . then the probability that he knew the answer is a/b where 'a' and 'b' are relatively prime . find the value of (a+b).

aditi jangid , 14 Years ago

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