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

 It is currently 27 Mar 2015, 21:21

### 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

# 4 elements are selected at random and with replacement from

 Question banks Downloads My Bookmarks Reviews Important topics
Author Message
TAGS:
GMAT Instructor
Joined: 04 Jul 2006
Posts: 1268
Followers: 23

Kudos [?]: 148 [0], given: 0

4 elements are selected at random and with replacement from [#permalink]  11 Aug 2006, 06:39
00:00

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
4 elements are selected at random and with replacement from the set {1/6, 1/4,1/3,1/2}. What is the probability that the sum of these elements will be an integer?
Senior Manager
Joined: 05 Mar 2006
Posts: 348
Followers: 1

Kudos [?]: 8 [0], given: 0

[#permalink]  11 Aug 2006, 07:08
OK, tell me what I'm doing wrong.

Number of possibilties: 4*4*4*4

Number of possibilites to sum up to an integer with 4 elements:

1) 4*(1/4) = 1, 1 combination

2) 4*(1/2) = 1, 1 combination

3) 2*(1/6) + 2*(1/3) = 1, 6 combinations (4c2)

therefore total combinations = 8

8/(4*4*4*4) = 1/32

Am I missing out other combinations?
CEO
Joined: 20 Nov 2005
Posts: 2913
Schools: Completed at SAID BUSINESS SCHOOL, OXFORD - Class of 2008
Followers: 18

Kudos [?]: 110 [0], given: 0

[#permalink]  11 Aug 2006, 07:30
Total cases = 4^4 = 256

Instead of this I will consider {2,3,4,6} and sum should be divisible by 12.

2,2,2,6 = 12-------Cases = 4
3,3,3,3 = 12-------Cases = 1
2,2,4,4 = 12-------Cases = 6
6,6,6,6 = 24-------Cases = 1

Prob = 12/256 = 3/64
_________________

SAID BUSINESS SCHOOL, OXFORD - MBA CLASS OF 2008

Senior Manager
Joined: 05 Mar 2006
Posts: 348
Followers: 1

Kudos [?]: 8 [0], given: 0

[#permalink]  11 Aug 2006, 07:36
Aha,

Thanks PS, I missed the combination of 3*(1/3) + 1/2

4c3 = 4 Combinations
Manager
Joined: 05 Jul 2006
Posts: 198
Followers: 1

Kudos [?]: 18 [0], given: 0

[#permalink]  16 Aug 2006, 16:12
PS can you explain how you arrive to these:

2,2,2,6 = 12-------Cases = 4
3,3,3,3 = 12-------Cases = 1
2,2,4,4 = 12-------Cases = 6
6,6,6,6 = 24-------Cases = 1
CEO
Joined: 20 Nov 2005
Posts: 2913
Schools: Completed at SAID BUSINESS SCHOOL, OXFORD - Class of 2008
Followers: 18

Kudos [?]: 110 [0], given: 0

[#permalink]  16 Aug 2006, 19:11
lan583 wrote:
PS can you explain how you arrive to these:

2,2,2,6 = 12-------Cases = 4
3,3,3,3 = 12-------Cases = 1
2,2,4,4 = 12-------Cases = 6
6,6,6,6 = 24-------Cases = 1

2,2,2,6
there are four cases
6,2,2,2
2,6,2,2
2,2,6,2
2,2,2,6
This can be calculated using 4!/3! = 4

Similarly for 3,3,3,3 there is only one case.

For 2,2,4,4 there are 6 cases
2,2,4,4
2,4,4,2
2,4,2,4
4,2,2,4
4,2,4,2
4,2,2,2
this can be calculated using 4!/(2!*2!) = 6

For 6,6,6,6 there is only one case.

Hope this helps.
_________________

SAID BUSINESS SCHOOL, OXFORD - MBA CLASS OF 2008

[#permalink] 16 Aug 2006, 19:11
Similar topics Replies Last post
Similar
Topics:
if two students are chosen at random with replacement from a 1 20 Mar 2011, 07:58
7 If two students are chosen at random with replacement from a 10 21 Jun 2008, 02:02
If a bottle is to be selected at random from a certain 2 19 Jun 2007, 21:41
If a bottle is to be selected at random from a certain 2 10 Feb 2006, 14:15
If two students are chosen at random with replacement from a 2 12 Oct 2005, 20:34
Display posts from previous: Sort by

# 4 elements are selected at random and with replacement from

 Question banks Downloads My Bookmarks Reviews Important topics

 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®.