It is currently 23 Oct 2017, 14:03

### 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

# 15 chess players take part in a tournament. Every player

Author Message
SVP
Joined: 04 May 2006
Posts: 1881

Kudos [?]: 1408 [0], given: 1

Schools: CBS, Kellogg
15 chess players take part in a tournament. Every player [#permalink]

### Show Tags

13 May 2008, 00:59
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

15 chess players take part in a tournament. Every player plays twice with each of his opponents. How many games are to be played?

190
200
210
220
225

The OE is difficult for me to understand!
_________________

Kudos [?]: 1408 [0], given: 1

CEO
Joined: 17 May 2007
Posts: 2947

Kudos [?]: 668 [0], given: 210

### Show Tags

13 May 2008, 01:09
C

Quite easy.

Whenever there is a problem such as this where there are n participants every participant plays everyone else , you can calculate the total number of games by the the series 1 + 2 + 3 + 4 + .. n-1

So in this case this series adds to 14 * 7.5 = 105 games. If they play each other twice, its 105 * 2 = 210 games.

sondenso wrote:
15 chess players take part in a tournament. Every player plays twice with each of his opponents. How many games are to be played?

190
200
210
220
225

The OE is difficult for me to understand!

Kudos [?]: 668 [0], given: 210

VP
Joined: 10 Jun 2007
Posts: 1434

Kudos [?]: 352 [0], given: 0

### Show Tags

13 May 2008, 06:38
sondenso wrote:
15 chess players take part in a tournament. Every player plays twice with each of his opponents. How many games are to be played?

190
200
210
220
225

The OE is difficult for me to understand!

C

Imagine you have 4 people, ABCD, and each player play with each other once.
In each arrangements, you have
AB, AC, AD => 3 total
BC, BD => 2 total
CD => 1 total
Total = 3 + 2 + 1
Do the same for 15 people...and you will have
14+13+12+...+1 = 105
Twice that, you get 105*2 = 210

Kudos [?]: 352 [0], given: 0

Current Student
Joined: 28 Dec 2004
Posts: 3349

Kudos [?]: 319 [0], given: 2

Location: New York City
Schools: Wharton'11 HBS'12

### Show Tags

13 May 2008, 11:28
yeah..i too get 210..

general formula for these type of problems is sum of 1 to (n-1)*Number of times each player plays a game..

Kudos [?]: 319 [0], given: 2

Manager
Joined: 01 May 2008
Posts: 111

Kudos [?]: 7 [0], given: 0

Location: São Paulo

### Show Tags

13 May 2008, 16:04
I did with a different formula:
15!/13! = 15*14 = 210

Kudos [?]: 7 [0], given: 0

Manager
Joined: 12 Feb 2008
Posts: 177

Kudos [?]: 46 [0], given: 0

### Show Tags

13 May 2008, 16:37
quote="ldpedroso"]I did with a different formula:
15!/13! = 15*14 = 210[/quote]

i did it in a similar way.
15*14 which is essentially 15!/13!

Kudos [?]: 46 [0], given: 0

SVP
Joined: 04 May 2006
Posts: 1881

Kudos [?]: 1408 [0], given: 1

Schools: CBS, Kellogg

### Show Tags

13 May 2008, 21:22
bsd_lover wrote:
Quite easy.

OA is C
_________________

Kudos [?]: 1408 [0], given: 1

Current Student
Joined: 28 Dec 2004
Posts: 3349

Kudos [?]: 319 [0], given: 2

Location: New York City
Schools: Wharton'11 HBS'12

### Show Tags

16 May 2008, 08:48
I should elaborate where this formula n*n-1 is comin from

basically the formula is ..well first..you need to 2 chess players to play 1 game correct!

with this assumption in mind you are asking yourself ..the total number of games played..well that really means NC2..i.e in how many ways can you choose 2 players out of N..

NC2=N*(N-1)/2=total number of games played!

now in this question we are told number of games played=2 times each..so basically this becomes (n)(n-1)=15*14=210

Kudos [?]: 319 [0], given: 2

SVP
Joined: 04 May 2006
Posts: 1881

Kudos [?]: 1408 [0], given: 1

Schools: CBS, Kellogg

### Show Tags

16 May 2008, 20:10
Warm-hearted fresiha12! Thanks!
_________________

Kudos [?]: 1408 [0], given: 1

Re: M11-29   [#permalink] 16 May 2008, 20:10
Display posts from previous: Sort by