use 26 character to make 3 characters password, only mid : PS Archive
Check GMAT Club Decision Tracker for the Latest School Decision Releases http://gmatclub.com/AppTrack

 It is currently 19 Jan 2017, 12:18

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

use 26 character to make 3 characters password, only mid

Author Message
Manager
Joined: 22 Apr 2003
Posts: 179
Followers: 2

Kudos [?]: 43 [0], given: 0

Show Tags

03 Dec 2003, 16:48
00:00

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions

HideShow timer Statistics

This topic is locked. If you want to discuss this question please re-post it in the respective forum.

use 26 character to make 3 characters password, only mid figure should be not tha same as the other two, ask number of password?

from China's site
Intern
Joined: 22 Nov 2003
Posts: 41
Location: Serbia
Followers: 0

Kudos [?]: 3 [0], given: 0

Show Tags

03 Dec 2003, 18:33
Number of passwords without "middle character" rule:
26*26*26

then we have to subtract number of forbidden passwords :

char X char (char = X ( only one character or both of them) )

there are 26*3 passwords like those mentioned above,
each of characters (26 ) has three forbiden passwords...when X is at first place of the password , when X is at last place and when is X at both places.
e.g. Forbiden passwords for letter A:
A A char
char A A
A A A

Finally, number of possible passwords is :
26 * ( 26*26 - 3 ) = 17 498

Senior Manager
Joined: 11 Nov 2003
Posts: 357
Location: Illinois
Followers: 1

Kudos [?]: 5 [0], given: 0

Show Tags

03 Dec 2003, 18:47
should this be calculated like this?

Total number = 25 x 26 x 25 = 16,250
Intern
Joined: 22 Nov 2003
Posts: 41
Location: Serbia
Followers: 0

Kudos [?]: 3 [0], given: 0

Show Tags

03 Dec 2003, 19:00
I am not sure...where did I make mistake?
My way is indirect, your solution is direct and easier..but I am not sure now what is right answer...
Intern
Joined: 22 Nov 2003
Posts: 41
Location: Serbia
Followers: 0

Kudos [?]: 3 [0], given: 0

Show Tags

03 Dec 2003, 19:17
I got it...there are not only 26 x 3 forbidden passwords...
A A char - 25
char A A - 25
A A A -1
multiplied by 26 ..26 x ( 26+25).....=1326
too complicated...
Well, it seems that I should go to sleep know...my brain doesn't work well anymore...it's 4 a.m. in my country
Bye!
SVP
Joined: 03 Feb 2003
Posts: 1603
Followers: 8

Kudos [?]: 245 [0], given: 0

Show Tags

04 Dec 2003, 07:36
my solution:

the total number is 26*26*26
the number of wrong combinations is 26*25*1

so, [26*26*26]–[26*25]=16926
Senior Manager
Joined: 02 Mar 2004
Posts: 327
Location: There
Followers: 1

Kudos [?]: 0 [0], given: 0

Show Tags

17 May 2004, 17:26
chihao wrote:
use 26 character to make 3 characters password, only mid figure should be not tha same as the other two, ask number of password?

case1: XYZ, where X and Z are the same.
26*25
case2: XYZ, where letters X and Z are different.
26*25*24

OR:
Lets fix Y: this can be in 26 ways.
X and Z are different from Y: This can be done in 25*25 ways.

Re: PS   [#permalink] 17 May 2004, 17:26
Display posts from previous: Sort by