Please solve ALL THREE questions! Thank you! A new secretary has been given n co
ID: 3209154 • Letter: P
Question
Please solve ALL THREE questions! Thank you!
A new secretary has been given n computer passwords, only one of which will permit access to a computer file. Because the secretary has no idea which password is correct, he chooses one of the passwords at random and tries it. If the password is incorrect, he discards it and randomly selects another password from among those remaining, proceeding in this manner until he finds the correct password. What is the probability that he obtains the correct password on the first try? What is the probability that he obtains the correct password on the second try? The third try? A security system has been set up so that if three incorrect passwords are tried before the correct one, the computer file is locked and access to it denied. If n = 7, what is the probability that the secretary will gain access to the file?Explanation / Answer
a) as there are n choices and only one favourable outcome
hence probability that he obtains the correct password on first try =1/n
b) probabilty that he obtains the correct password on the second try =P(he misses on first and got password right on second)=((n-1)/n)*(1/(n-1)) =1/n
similarly he obtains the correct password on the second try =1/n
c)probabilty that he gains access to the file =P(he gets acces on first attempt +gets access on 2nd +gets access on 3rd attempt)=(1/7)+(1/7)+(1/7) =3/7