Last visit was: 23 May 2026, 17:51 It is currently 23 May 2026, 17:51
Home
Messages
Tests
Schools
Events
Close
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
Your Progress

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
Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.
Go to My Error Log Learn more
Close
Request Expert Reply
Confirm Cancel
User avatar
IrinaOK
User avatar
Joined: 22 Aug 2007
Last visit: 01 Jan 2008
Posts: 275
Own Kudos:
511
Posts: 275
Kudos: 511
GMATprep_probability 30 Oct 2007, 00:29
Kudos
Add Kudos
Bookmarks
Bookmark this Post
thanks



Archived Topic
Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Quantitative Questions Forum
Still interested in this question? Check out the "Best Topics" block below for a better discussion on this exact question, as well as several more related questions.
Thank you for understanding, and happy exploring!
User avatar
ywilfred
User avatar
Joined: 07 Jul 2004
Last visit: 06 Mar 2012
Posts: 1,987
Own Kudos:
2,054
Location: Singapore
Posts: 1,987
Kudos: 2,054
GMATprep_probability 30 Oct 2007, 01:51
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Letter A,B,C,D
Envelope a,b,c,d

Assume Letter A goes to envelope a.
For envelope B, we can only place letter C or D --> 2 ways (assume letter C goes to envelope b)
For envelope C, we can only place letter D --> 1 way
For envelope D, we place the last letter, letter B --> 1 way

# of ways --> 2

There are also cases for letter B to envelope b, letter C to envelope c, and letter D to envelope d. Total # of winning solutions = 8

# of ways to place the letters = 4! = 24

P = 8/24 = 1/3

Ans D
User avatar
alimad
User avatar
Joined: 10 Feb 2006
Last visit: 09 Jul 2014
Posts: 466
Own Kudos:
4,449
Posts: 466
Kudos: 4,449
GMATprep_probability 30 Oct 2007, 07:37
Kudos
Add Kudos
Bookmarks
Bookmark this Post
ywilfred, my prob skills are quite weak. Can you break down how you got the 8, out of the 24 probable combination.

I know there are 4 valid combination A-A, B-B,C-C,D-D. I'm just not getting the rest. Thanks for you help.
User avatar
alimad
User avatar
Joined: 10 Feb 2006
Last visit: 09 Jul 2014
Posts: 466
Own Kudos:
4,449
Posts: 466
Kudos: 4,449
GMATprep_probability 30 Oct 2007, 07:44
Kudos
Add Kudos
Bookmarks
Bookmark this Post
oK, my bad, read it incorrectly :

A ----- > B,C,D ----- > 3
B ---- > C, D ---- > 2
C ---- > D ---- > 1

So I'm getting 6 that won't match....
User avatar
IrinaOK
User avatar
Joined: 22 Aug 2007
Last visit: 01 Jan 2008
Posts: 275
Own Kudos:
511
Posts: 275
Kudos: 511
GMATprep_probability 30 Oct 2007, 15:59
Kudos
Add Kudos
Bookmarks
Bookmark this Post
ywilfred
Letter A,B,C,D
Envelope a,b,c,d

Assume Letter A goes to envelope a.
For envelope B, we can only place letter C or D --> 2 ways (assume letter C goes to envelope b)
For envelope C, we can only place letter D --> 1 way
For envelope D, we place the last letter, letter B --> 1 way

# of ways --> 2

There are also cases for letter B to envelope b, letter C to envelope c, and letter D to envelope d. Total # of winning solutions = 8

# of ways to place the letters = 4! = 24

P = 8/24 = 1/3

Ans D
Show more


Hello ywilfred,

I got my mistake. Thank you :)
User avatar
IrinaOK
User avatar
Joined: 22 Aug 2007
Last visit: 01 Jan 2008
Posts: 275
Own Kudos:
511
Posts: 275
Kudos: 511
GMATprep_probability 30 Oct 2007, 16:00
Kudos
Add Kudos
Bookmarks
Bookmark this Post
alimad
oK, my bad, read it incorrectly :

A ----- > B,C,D ----- > 3
B ---- > C, D ---- > 2
C ---- > D ---- > 1

So I'm getting 6 that won't match....
Show more


A-----> a-----------> 1 way
B-----> c,d---------> 2 ways (letter B can`t go to a or b)
C-----> d-----------> 1 way (letter C can`t go to a or c or b, if letter C goes to b then only envelop d would be left for letter D-not winning case)
D-----> b-----------> 1 way (one envelop is left)

for each letter in correct envelop there are 1*2*1*1 ways to organize the rest letters and envelops, so that none matches.

4*2=8

can it be solved by formulas, without listing...?

while listing i made mistake, i thought C can go to either d or b envelop, and got 4*4=16 # winning case.. got stuck there

OA is D :)



Archived Topic
Hi there,
This topic has been closed and archived due to inactivity or violation of community quality standards. No more replies are possible here.
Where to now? Join ongoing discussions on thousands of quality questions in our Quantitative Questions Forum
Still interested in this question? Check out the "Best Topics" block above for a better discussion on this exact question, as well as several more related questions.
Thank you for understanding, and happy exploring!