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

It is currently 25 Aug 2016, 18:26
GMAT Club Tests

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

How many triangles can be formed using 8 points in a given p

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

1 KUDOS received
Manager
Manager
avatar
Joined: 20 Aug 2009
Posts: 107
Followers: 2

Kudos [?]: 106 [1] , given: 31

How many triangles can be formed using 8 points in a given p [#permalink]

Show Tags

New post 23 Aug 2009, 05:46
1
This post received
KUDOS
10
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  35% (medium)

Question Stats:

59% (01:32) correct 41% (00:47) wrong based on 558 sessions

HideShow timer Statistics

How many triangles can be formed using 8 points in a given plane?

(1) A triangle is formed by joining 3 distinct points in the plane
(2) Out of 8 given points, three are collinear
[Reveal] Spoiler: OA
5 KUDOS received
Senior Manager
Senior Manager
avatar
Joined: 27 May 2009
Posts: 281
Followers: 2

Kudos [?]: 264 [5] , given: 18

Re: Permutations 1 [#permalink]

Show Tags

New post 23 Aug 2009, 06:08
5
This post received
KUDOS
1
This post was
BOOKMARKED
IMO B. 8c3 - 1

A is the general stmt. we know that Triangle is fromed using only 3 points.
Manager
Manager
User avatar
Joined: 14 Aug 2009
Posts: 123
Followers: 2

Kudos [?]: 99 [0], given: 13

Re: Permutations 1 [#permalink]

Show Tags

New post 23 Aug 2009, 08:55
rohansherry wrote:
IMO B. 8c3 - 1

A is the general stmt. we know that Triangle is fromed using only 3 points.


Good one! kudos goes to you.
_________________

Kudos me if my reply helps!

Senior Manager
Senior Manager
avatar
Joined: 27 May 2009
Posts: 281
Followers: 2

Kudos [?]: 264 [0], given: 18

Re: Permutations 1 [#permalink]

Show Tags

New post 23 Aug 2009, 12:17
flyingbunny wrote:
rohansherry wrote:
IMO B. 8c3 - 1

A is the general stmt. we know that Triangle is fromed using only 3 points.


Good one! kudos goes to you.



thanks ya... was wondering when will i get my first kudos
Manager
Manager
User avatar
Joined: 14 Aug 2009
Posts: 123
Followers: 2

Kudos [?]: 99 [0], given: 13

Re: Permutations 1 [#permalink]

Show Tags

New post 23 Aug 2009, 18:19
1
This post was
BOOKMARKED
The meaning of "8C3-1" is really brief, clear and precise. That is the beauty of math. I like it and you deserve a kudos for this. :)
_________________

Kudos me if my reply helps!

Senior Manager
Senior Manager
User avatar
Joined: 20 Mar 2008
Posts: 454
Followers: 1

Kudos [?]: 108 [0], given: 5

Re: Permutations 1 [#permalink]

Show Tags

New post 23 Aug 2009, 21:09
rohansherry wrote:
IMO B. 8c3 - 1

A is the general stmt. we know that Triangle is fromed using only 3 points.


Agree with B. But I think the combination formula might be wrong.

IMHO, only 3 points are collinear, all the other 5 points are not on the same line. Hence, each of the 3 points can be combined with 2 of the 5 points to create a triangle.

Therefore, the # of triangles = 3 x 5C2 = 3 x 10 = 30.

Last edited by Jivana on 23 Aug 2009, 21:22, edited 1 time in total.
Manager
Manager
User avatar
Joined: 14 Aug 2009
Posts: 123
Followers: 2

Kudos [?]: 99 [0], given: 13

Re: Permutations 1 [#permalink]

Show Tags

New post 23 Aug 2009, 21:20
Jivana wrote:
rohansherry wrote:
IMO B. 8c3 - 1

A is the general stmt. we know that Triangle is fromed using only 3 points.


Agree with B. But I think the combination formula might be wrong.

IMHO, only 3 points are collinear, all the other 5 points are not on the same line. Hence, each of the 3 points can be combined with 2 of the 5 points to create a triangle.

Therefore, the # of triangles = 3 x 5C3 = 3 x 10 = 30.


You forgot 2 of the 3 points (collinear) and 1 of the 5 points to form a triangle.
_________________

Kudos me if my reply helps!

Senior Manager
Senior Manager
User avatar
Joined: 20 Mar 2008
Posts: 454
Followers: 1

Kudos [?]: 108 [0], given: 5

Re: Permutations 1 [#permalink]

Show Tags

New post 23 Aug 2009, 21:26
Yep, I did indeed forget that.

# should be: 3 x 5C3 + 5 x 3C2 = 3 x 10 + 5 x 3 = 45.
Senior Manager
Senior Manager
avatar
Joined: 27 May 2009
Posts: 281
Followers: 2

Kudos [?]: 264 [0], given: 18

Re: Permutations 1 [#permalink]

Show Tags

New post 24 Aug 2009, 00:32
Jivana wrote:
Yep, I did indeed forget that.

# should be: 3 x 5C3 + 5 x 3C2 = 3 x 10 + 5 x 3 = 45.



I just feel you are missing here something.... Can yo explain how you comingup with this "3 x 5C3 + 5 x 3C2 = 3 x 10 + 5 x 3 = 45"
Director
Director
User avatar
Joined: 01 Apr 2008
Posts: 898
Name: Ronak Amin
Schools: IIM Lucknow (IPMX) - Class of 2014
Followers: 26

Kudos [?]: 556 [0], given: 18

Re: Permutations 1 [#permalink]

Show Tags

New post 24 Aug 2009, 07:48
rohansherry wrote:
Jivana wrote:
Yep, I did indeed forget that.

# should be: 3 x 5C3 + 5 x 3C2 = 3 x 10 + 5 x 3 = 45.



I just feel you are missing here something.... Can yo explain how you comingup with this "3 x 5C3 + 5 x 3C2 = 3 x 10 + 5 x 3 = 45"

Yup. It is not necessary to select ATLEAST one point from the three collinear points (as per the above equation)
SO we have to add 5C3 = 10 too.

So answer is 45+10 = 55 (Using Jivana's conventional method) and 8C3-1=56-1=55 (Using rohansherry's method faster method) :)
Manager
Manager
User avatar
Joined: 14 Aug 2009
Posts: 123
Followers: 2

Kudos [?]: 99 [0], given: 13

Re: Permutations 1 [#permalink]

Show Tags

New post 24 Aug 2009, 07:57
Economist wrote:
rohansherry wrote:
Jivana wrote:
Yep, I did indeed forget that.

# should be: 3 x 5C3 + 5 x 3C2 = 3 x 10 + 5 x 3 = 45.



I just feel you are missing here something.... Can yo explain how you comingup with this "3 x 5C3 + 5 x 3C2 = 3 x 10 + 5 x 3 = 45"

Yup. It is not necessary to select ATLEAST one point from the three collinear points (as per the above equation)
SO we have to add 5C3 = 10 too.

So answer is 45+10 = 55 (Using Jivana's conventional method) and 8C3-1=56-1=55 (Using rohansherry's method faster method) :)


I believe it is the fastest. :-D
_________________

Kudos me if my reply helps!

Senior Manager
Senior Manager
User avatar
Joined: 20 Mar 2008
Posts: 454
Followers: 1

Kudos [?]: 108 [0], given: 5

Re: Permutations 1 [#permalink]

Show Tags

New post 24 Aug 2009, 13:43
Agreed, 8C3 - 1 is the best method.
Intern
Intern
avatar
Joined: 30 Jun 2009
Posts: 48
Followers: 1

Kudos [?]: 9 [0], given: 2

Re: Permutations 1 [#permalink]

Show Tags

New post 25 Aug 2009, 06:35
HI Guys, My answer would also be B.
But, I am not clear in the possibilities to form triangles.
1. using the 3 non collinear : 5C3
2. using one collinear and 2 non collinear : 3C1x5C2

I am sure that I am missing something here.
Would you please be of any help to understand the 55 possibilities?

Rgds
Intern
Intern
avatar
Joined: 30 Jun 2009
Posts: 48
Followers: 1

Kudos [?]: 9 [0], given: 2

Re: Permutations 1 [#permalink]

Show Tags

New post 25 Aug 2009, 06:39
Guys,

I just noticed that I was missing the 2 of the 3 points (collinear) and 1 of the 5 points

Thx
Intern
Intern
avatar
Joined: 30 Jun 2009
Posts: 48
Followers: 1

Kudos [?]: 9 [0], given: 2

Re: Permutations 1 [#permalink]

Show Tags

New post 25 Aug 2009, 06:41
Can someone please explain the "8C3 - 1" method.
What does this "-1" stands for?

Rgds
Manager
Manager
User avatar
Joined: 14 Aug 2009
Posts: 123
Followers: 2

Kudos [?]: 99 [0], given: 13

Re: Permutations 1 [#permalink]

Show Tags

New post 25 Aug 2009, 07:16
defoue wrote:
Can someone please explain the "8C3 - 1" method.
What does this "-1" stands for?

Rgds


the triangle by three points that are collinear.
_________________

Kudos me if my reply helps!

2 KUDOS received
Senior Manager
Senior Manager
avatar
Joined: 27 May 2009
Posts: 281
Followers: 2

Kudos [?]: 264 [2] , given: 18

Re: Permutations 1 [#permalink]

Show Tags

New post 25 Aug 2009, 07:19
2
This post received
KUDOS
1
This post was
BOOKMARKED
defoue wrote:
Can someone please explain the "8C3 - 1" method.
What does this "-1" stands for?

Rgds


hey see,

if have to make all triangles from n points...then it would be nc3.....because triangle has 3 sides.... so out of n any 3 sides...

now 3 point are colinear so we cant make one triangle...so we se subtract that from it..


hope its clear....now
1 KUDOS received
Intern
Intern
avatar
Joined: 30 Jun 2009
Posts: 48
Followers: 1

Kudos [?]: 9 [1] , given: 2

Re: Permutations 1 [#permalink]

Show Tags

New post 26 Aug 2009, 04:59
1
This post received
KUDOS
rohansherry wrote:
defoue wrote:
Can someone please explain the "8C3 - 1" method.
What does this "-1" stands for?

Rgds


hey see,

if have to make all triangles from n points...then it would be nc3.....because triangle has 3 sides.... so out of n any 3 sides...

now 3 point are colinear so we cant make one triangle...so we se subtract that from it..


hope its clear....now


Cristal clear
Thx very much
Manager
Manager
avatar
Joined: 20 Aug 2009
Posts: 107
Followers: 2

Kudos [?]: 106 [0], given: 31

Re: Permutations 1 [#permalink]

Show Tags

New post 26 Aug 2009, 05:27
Guys, I am sorry that it took me so long to post the OA. But here it is:

1. is insufficient because it just states a well known fact
2. is sufficient because in such case we can calculate the number of triangles that can be formed: 5C3+8*3C2+3C1*5C2

__________________________________
Please kudos me if you find my post useful
Intern
Intern
User avatar
Joined: 19 Mar 2013
Posts: 23
Followers: 0

Kudos [?]: 3 [0], given: 27

Re: Problem: triangle in a plane Level: Medium How many [#permalink]

Show Tags

New post 10 Dec 2013, 06:09
Why can't we just pick all possible combinations of 3 points out of 8 to answer the first question?
8C3 looks sufficient to me
please help
Re: Problem: triangle in a plane Level: Medium How many   [#permalink] 10 Dec 2013, 06:09

Go to page    1   2    Next  [ 25 posts ] 

    Similar topics Author Replies Last post
Similar
Topics:
Experts publish their posts in the topic In an isosceles triangle PQR, how many degrees is ∠ P Bunuel 3 27 May 2016, 09:09
4 Experts publish their posts in the topic Point P is a point inside triangle ABC. Is triangle ABC equilateral? mikemcgarry 1 24 May 2016, 15:08
50 Experts publish their posts in the topic How many different 5-person teams can be formed from a group gmatJP 14 22 Jun 2010, 19:14
15 Experts publish their posts in the topic In how many ways can 3-digit numbers be formed selecting 3 d GODSPEED 19 16 Aug 2009, 04:13
11 Experts publish their posts in the topic S is a set of points in the plane. How many distinct triangles can be GGUY 14 15 Mar 2008, 00:41
Display posts from previous: Sort by

How many triangles can be formed using 8 points in a given p

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| 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®.