Assume there are 6 versions of an exam being handed out by a

Assume there are 6 versions of an exam being handed out by a professor. What are the chances that the next 4 exams handed out will be the same version? (Assume exams are mutually exclusive i.e passing out one version 1 exam does not reduce probability of another version 1 exam also being handed out)

Solution

Probability of one of the version being handed out is 1/6

So first we need to choose one of the versions which will be handed out in next 4 exams

This is done in C(6,4)=6*5/2=15 ways

So required probablity is :15/6^4=5/432