ISRO 2009-ECE Probability

Question

A man with n keys wants to open a lock. He tries his keys at random.

The expected number of attempts for his success is (keys are replaced after every attempt)

a) n/2

b) n

c) √ n

d) None of the above

Comments

here we are asked number of trials and whenever no of trails are asked it is geometric distribution.

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Thanks @sushmita. 

https://en.wikipedia.org/wiki/Geometric_distribution?wprov=sfla1

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@sushmita,is it true in every case??