Find all School-related info fast with the new School-Specific MBA Forum

It is currently 25 Oct 2014, 14:26

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.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

Tanya prepared 4 different letters to be sent to 4 different

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Senior Manager
Senior Manager
avatar
Joined: 23 May 2005
Posts: 266
Location: Sing/ HK
Followers: 1

Kudos [?]: 14 [0], given: 0

Tanya prepared 4 different letters to be sent to 4 different [#permalink] New post 10 Dec 2006, 07:28
Tanya prepared 4 different letters to be sent to 4 different addresses. For each letter, she prepared an envelope with its correct address. If the 4 letters are to be put into the 4 envelopes at random, what is the probability that exactly 2 letters will be put into 2 envelopes with its correct address?
_________________

Impossible is nothing

Kaplan Promo CodeKnewton GMAT Discount CodesManhattan GMAT Discount Codes
Senior Manager
Senior Manager
avatar
Joined: 20 Feb 2006
Posts: 375
Followers: 1

Kudos [?]: 1 [0], given: 0

 [#permalink] New post 10 Dec 2006, 07:36
Is it 1/4?

Chance of 1st letter being correct = 1/4
Chance of 2nd letter being correct = 1/3
Chance of 3rd letter being incorrect = 1/2
Chance of 4th letter being incorrect =1

1/4 * 1/3 * 1/2 * 1 = 1/24

No of ways of choosing 2 letters from 4 = 4C2 = 6

6*1/24 = 1/4

Where is the question from?
Senior Manager
Senior Manager
avatar
Joined: 23 May 2005
Posts: 266
Location: Sing/ HK
Followers: 1

Kudos [?]: 14 [0], given: 0

 [#permalink] New post 10 Dec 2006, 10:21
I also got 1/4 :-)

The original question is from GMATprep but I changed it a bit to spice things up. Wanted to check if I fully understood the concept :-)
_________________

Impossible is nothing

Manager
Manager
avatar
Joined: 04 Feb 2004
Posts: 71
Location: India
Followers: 1

Kudos [?]: 25 [0], given: 0

 [#permalink] New post 10 Dec 2006, 11:32
is 1/4 the correct answer though ? - the question said any two letters need to be correctly addressed not the first two ....

this is what I got ...
number of ways 4 letters could be arranged in 4 envelopes = !4 = 24

let any of the two letters be correctlu put into the envelope ,
Now the number of ways the rest two letters could be put = !2 = 2

So, the required probability is 2/24 = 1/12

please let me know .....
Senior Manager
Senior Manager
avatar
Joined: 20 Feb 2006
Posts: 375
Followers: 1

Kudos [?]: 1 [0], given: 0

 [#permalink] New post 10 Dec 2006, 12:17
I tabulated the possibilities and for any two to be correct the answer is 1/4
Senior Manager
Senior Manager
avatar
Joined: 14 Aug 2006
Posts: 368
Followers: 1

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

 [#permalink] New post 10 Dec 2006, 14:15
I get a different answer..

The total number of possibilities : 24 (4p4)
4 envelopes and 4 letters

The possibility that 1 and 2 envelope has the right letters = 2P2 = 2

There are a total of 7 such possibilities: 12, 13, 14, 23, 24, 34, 14 : 14


The probability : 14/24 = 7/12

The OA please??
Senior Manager
Senior Manager
avatar
Joined: 20 Feb 2006
Posts: 375
Followers: 1

Kudos [?]: 1 [0], given: 0

 [#permalink] New post 10 Dec 2006, 15:19
There is no OA cos adaptation of GMAT prep question that asks same thing but for 1 letter in correct position. I've drawn a table of all posibilities - correct answer is 1/4

I've labelled envelopes, 1,2,3,4 with correct letter being A=1, B=2, C=3, D=4
Attachments

ProbTable.doc [54 KiB]
Downloaded 37 times

To download please login or register as a user

Senior Manager
Senior Manager
avatar
Joined: 14 Aug 2006
Posts: 368
Followers: 1

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

 [#permalink] New post 10 Dec 2006, 16:28
I agree... That is a concrete way to prove something :-)


My mistake..

i took in to the choices when all 4 are correct into the count..
Senior Manager
Senior Manager
avatar
Joined: 20 Feb 2006
Posts: 375
Followers: 1

Kudos [?]: 1 [0], given: 0

 [#permalink] New post 10 Dec 2006, 16:49
I still wonder about the method:

Maybe it should be total no. of ways = 4! = 24
No of unique ways to choose letters = 4C2 = 6

6/24=1/4?

Maybe one of the math gurus could help -- Fig?
Manager
Manager
avatar
Joined: 04 Feb 2004
Posts: 71
Location: India
Followers: 1

Kudos [?]: 25 [0], given: 0

 [#permalink] New post 10 Dec 2006, 20:44
No I agree it should be 1/4 ...


4C2/ 4! = 6/24 = 1/4

The number of ways any two letters can be correctly put out of total 4 envelopes should be 4C2 ...

Thanks MBAlad !
Senior Manager
Senior Manager
avatar
Joined: 20 Feb 2006
Posts: 375
Followers: 1

Kudos [?]: 1 [0], given: 0

 [#permalink] New post 11 Dec 2006, 08:44
Thanks. I'm just wondering if the original way I calculated it (1/4*1/3*1/2*1*4C2=1/4) is a sound method.
Senior Manager
Senior Manager
avatar
Joined: 08 Jun 2006
Posts: 343
Location: Washington DC
Followers: 1

Kudos [?]: 14 [0], given: 0

 [#permalink] New post 11 Dec 2006, 11:03
Getting 1 / 4

Total number of cases - 4! = 24
Combination of 2 letters = 4 C 2 = 6
Putting 2 letters in correct address can happen only in one way = 6 * 1 = 6

So 6/24 = 1/4
Director
Director
avatar
Joined: 01 Oct 2006
Posts: 500
Followers: 1

Kudos [?]: 16 [0], given: 0

 [#permalink] New post 11 Dec 2006, 11:14
anindyat wrote:
Getting 1 / 4

Total number of cases - 4! = 24
Combination of 2 letters = 4 C 2 = 6
Putting 2 letters in correct address can happen only in one way = 6 * 1 = 6

So 6/24 = 1/4


agree with anidya it must be 1/4
  [#permalink] 11 Dec 2006, 11:14
    Similar topics Author Replies Last post
Similar
Topics:
1 Tanya prepared 4 different letters to be sent to 4 different tarek99 6 27 Oct 2008, 09:54
Tanya prepared 4 different letters to be sent to 4 different nitinneha 2 04 Apr 2007, 16:06
Tanya prepared 4 different letters to be sent to 4 different artshep 4 17 Nov 2006, 15:34
16 Experts publish their posts in the topic Tanya prepared 4 letters to be sent to 4 different tealeaflin 11 15 Oct 2006, 13:12
Tanya prepared 4 different letters to be sent to 4 different positive_energy 5 11 Aug 2006, 04:41
Display posts from previous: Sort by

Tanya prepared 4 different letters to be sent to 4 different

  Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group and phpBB SEO

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.