Use these to find E & V.
A secretary was given n passwords and tries the passwords at random. Exactly one password will permit access to a computer file. Find the mean and variance of Y, the number of trials required to open the file, if unsuccessful passwords are eliminated.
What I have for this question is that the probability of getting the password right on:
the 1st try=1/n
2nd try=1/n
3rd try=1/n
so thus the mean is:
=1(1/n)+2(1/n)+3(1/n)+y(1/n)
= 1+2+3+4+y
n
is this right or can i go further?
thanks