Probabilities

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mariofelixpasku: Senior | Next Rank: 100 Posts; Posts: 41; Joined: Sun Sep 23, 2012 4:26 am; Thanked: 2 times

by mariofelixpasku » Mon Oct 22, 2012 11:29 am

On an examination there are 25 different topics and only 3 questions. A student did not have enough time to prepare for 10 of the topics. What is the probability that he will be able to answer all three questions on the exam?

A: 91/120

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Source: Beat The GMAT — Problem Solving | Mon Oct 22, 2012 11:29 am

vikram4689: Legendary Member; Posts: 1325; Joined: Sun Nov 01, 2009 6:24 amFollowed by: 14 members; Thanked: 105 times

by vikram4689 » Mon Oct 22, 2012 6:16 pm

what is the source of this question. your answer seems incorrect.

student has prepared 15 topics and if all 3 question are from these 15 then she will be able to solve.

P=15/25 * 14/24 * 13/23 = 91/460

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