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04 May 2020, 05:23
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Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!
Difficulty:
55%
(hard)
Question Stats:
69% (02:40) correct
31%
(02:57)
wrong
based on 104
sessions
History
Date
Time
Result
Not Attempted Yet
Members of a certain website are required to select passwords that are exactly six characters long. The first four characters may be selected from any of the 26 letters from A to Z (not case-sensitive) or any of the digits 0-9, but the last two characters of the password must be selected from only the digits 0-9. For Instance, abcd45, 8hi976. and 5dog56 are valid passwords. A hacker writes a computer program mat will test every permissible password combination at a rate of 72 passwords per second. How long, IN HOURS, will it take the hacker's program to test every permissible password combination?
A. 18
B. 62
C. 648
D. 1,080
E. 38,880
Are You Up For the Challenge: 700 Level Questions
A. 18
B. 62
C. 648
D. 1,080
E. 38,880
Are You Up For the Challenge: 700 Level Questions
04 May 2020, 12:04
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Bunuel
- Character of password = 6
- Note:- there is no restriction of repetition of character
The number of ways in which first four characters can be selected = \(36C1*36C1*36C1*36C1=36*36*36*36\)
The number of ways in which last two characters of password can be selected = \(10C1*10C1=10*10\)
- Total number of ways of selecting password = \(36*36*36*36*10*10\)
Number of hours in hacking password = \(\frac{36*36*36*36*10*10}{72*60*60} = 648\).
04 May 2020, 12:15
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Bunuel
Solution
- • Since it is not mentioned that letters or digits cannot repeat, so considering the case when digits and characters can repeat.
- o The number of ways in which first 4 characters can be selected \(= 36^4 = 51*35*33\)
o The number of ways in which last two character can be selected \(= 10^2 = 45\)
o So, total number of possible passwords \(= 36^4*10^2\)
