combination question from the gmatclub lesson

Oldest

Best Reply

Author

Message

TAGS:

Senior Manager

Joined: 06 Jul 2004

Posts: 480

Location: united states

Followers: 1

Kudos [?]: 6 [0], given: 0

combination question from the gmatclub lesson [#permalink]

27 Jun 2006, 12:30

Guys,

this question is from the "combinations lessons" on this website.

http://www.gmatclub.com/content/courses ... ations.php

EXAMPLE 11. There are 11 top managers that need to form a decision group. How many ways are there to form a group of 5 if the President and Vice President are not to serve on the same team?

Well, the President and the V President are not supposed to be in the same team. So, we effectively have 10 people to make a group of 5. This gives us

10!/(5!*5!) = 252.

so, 252 teams can be formed by including VP or President. So, the total number of teams = 252*2
= 504

The answer is different than what the author got. Where am i wrong?
_________________

for every person who doesn't try because he is
afraid of loosing , there is another person who
keeps making mistakes and succeeds..

Kaplan GMAT Prep Discount Codes

Knewton GMAT Discount Codes

GMAT Pill GMAT Discount Codes

Senior Manager

Joined: 07 Jul 2005

Posts: 407

Location: Sunnyvale, CA

Followers: 2

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

[#permalink]

27 Jun 2006, 12:54

You have counted the scenario twice where both President and VPwill not be on the team. So, you need to subtract that from your answer..

#ways in which we can form a group of 5 without considering both VP/P : 9C5 = 126

504 - 126
= 378
This shd match with the original answer.

Senior Manager

Joined: 06 Jul 2004

Posts: 480

Location: united states

Followers: 1

Kudos [?]: 6 [0], given: 0

[#permalink]

27 Jun 2006, 19:01

i thought about it from a different angle this time.

there are 11 people. there are president, vice president and 9 other people. a team of 5 needs to be formed and president and vice president can't be in the same team.

scenario 1
------------
4 places in the team needs to be filled from 9 people.
1 place needs to be filled from 2 people.

number of ways = 2* (9C4) = 2*126 = 252

scenario 2
------------
5 places in the team to be filled by 9 people. president and v president are booted out

number of ways = 9C5 = 126

total number of ways = 378
_________________

for every person who doesn't try because he is
afraid of loosing , there is another person who
keeps making mistakes and succeeds..

CEO

Joined: 20 Nov 2005

Posts: 2934

Schools: Completed at SAID BUSINESS SCHOOL, OXFORD - Class of 2008

Followers: 7

Kudos [?]: 38 [0], given: 0

[#permalink]

27 Jun 2006, 19:40

shoonya wrote:

number of ways = 9C5 = 126

total number of ways = 378

Thats exactly the way I solved it. 2 * 9C4 + 9C5 = 378
_________________

SAID BUSINESS SCHOOL, OXFORD - MBA CLASS OF 2008

[#permalink] 27 Jun 2006, 19:40

		Similar topics	Author	Replies	Last post
Similar Topics:		Counting Problem frmo Combination Lessons	ywilfred	2	29 Jul 2004, 10:05
		From the gmatclub lessons: There are 5 married couples and a	stuti	1	09 Sep 2004, 22:55
		Practice Problem 2. from Combinations Lesson	nalle-b	6	17 Jul 2007, 08:41
		Lessons on Verbal and Math on GMATCLUB wanted!!!	Whatever	5	28 Oct 2007, 18:46
	1	Lessons from a rookie	AdrianPeterson	2	24 Jan 2009, 21:21

combination question from the gmatclub lesson

Main navigation

GMAT Resources

Partners

MBA Resources

GMAT ® is a registered trademark of the Graduate Management Admission Council ® (GMAC ®). GMAT Club's website has not been reviewed or endorsed by GMAC.

GMAT Courses

Admissions Consulting

combination question from the gmatclub lesson

combination question from the gmatclub lesson

Main navigation

GMAT Resources

Partners

MBA Resources