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tricky and tough prob gmat qustion

Expert replies
by quantskillsgmat » Wed Dec 14, 2011 1:19 am
If we have an empty room, and every week there is a 0.6 probability for a person to join, 0.2 probability for a person to leave, and 0.2 probability for no change (only one action can be performed per week and actions are as per given sequence), what is the probability that there are at least 40 people in the room after 104 weeks?

(A) 0.42
(B) 0.55
(C) 0.61
(D) 0.67
(E) 0.74
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Source: — Problem Solving |

by Shalabh7 » Thu Dec 15, 2011 12:09 pm
Source of the question ?

Initially the room is empty, so how can the probability of a person leaving be .2 ?
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