permutation
This topic has expert replies
- Md.Nazrul Islam
- Senior | Next Rank: 100 Posts
- Posts: 32
- Joined: Sat Jul 16, 2011 11:31 am
The number of parallelograms that can be formed from a set of four parallel straight line intersecting a set of three parallel straight lines .
- sanju09
- GMAT Instructor
- Posts: 3650
- Joined: Wed Jan 21, 2009 4:27 am
- Location: India
- Thanked: 267 times
- Followed by:80 members
- GMAT Score:760
Md.Nazrul Islam wrote:The number of parallelograms that can be formed from a set of four parallel straight line intersecting a set of three parallel straight lines .
I think I tried this in hurry. Please ignore my post and go with Mitch's explanation given below. The correct answer is [spoiler]18[/spoiler].
Last edited by sanju09 on Wed Apr 04, 2012 2:03 am, edited 1 time in total.
The mind is everything. What you think you become. -Lord Buddha
Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001
www.manyagroup.com
Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001
www.manyagroup.com
- GMATGuruNY
- GMAT Instructor
- Posts: 15539
- Joined: Tue May 25, 2010 12:04 pm
- Location: New York, NY
- Thanked: 13060 times
- Followed by:1906 members
- GMAT Score:790
From the set of 4 parallel lines:Md.Nazrul Islam wrote:The number of parallelograms that can be formed from a set of four parallel straight line intersecting a set of three parallel straight lines .
We need to choose a combination of 2 to serve as 2 parallel sides of the parallelogram.
The number of combinations of 2 that can formed from 4 choices = 4C2 = 6.
From the set of 3 parallel lines:
We need to choose a combination of 2 to serve as the OTHER 2 parallel sides of the parallelogram.
The number of combinations of 2 that can be formed from 3 choices = 3C2 = 3.
To combine the options above, we multiply:
6*3 = 18.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.
As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.
For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
We use combinations and not permutations because we can`t change the order of the lines, right??!GMATGuruNY wrote:From the set of 4 parallel lines:Md.Nazrul Islam wrote:The number of parallelograms that can be formed from a set of four parallel straight line intersecting a set of three parallel straight lines .
We need to choose a combination of 2 to serve as 2 parallel sides of the parallelogram.
The number of combinations of 2 that can formed from 4 choices = 4C2 = 6.
From the set of 3 parallel lines:
We need to choose a combination of 2 to serve as the OTHER 2 parallel sides of the parallelogram.
The number of combinations of 2 that can be formed from 3 choices = 3C2 = 3.
To combine the options above, we multiply:
6*3 = 18.
- sanju09
- GMAT Instructor
- Posts: 3650
- Joined: Wed Jan 21, 2009 4:27 am
- Location: India
- Thanked: 267 times
- Followed by:80 members
- GMAT Score:760
We use combination because we need to chose.ka_t_rin wrote:We use combinations and not permutations because we can`t change the order of the lines, right??!GMATGuruNY wrote:From the set of 4 parallel lines:Md.Nazrul Islam wrote:The number of parallelograms that can be formed from a set of four parallel straight line intersecting a set of three parallel straight lines .
We need to choose a combination of 2 to serve as 2 parallel sides of the parallelogram.
The number of combinations of 2 that can formed from 4 choices = 4C2 = 6.
From the set of 3 parallel lines:
We need to choose a combination of 2 to serve as the OTHER 2 parallel sides of the parallelogram.
The number of combinations of 2 that can be formed from 3 choices = 3C2 = 3.
To combine the options above, we multiply:
6*3 = 18.
The mind is everything. What you think you become. -Lord Buddha
Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001
www.manyagroup.com
Sanjeev K Saxena
Quantitative Instructor
The Princeton Review - Manya Abroad
Lucknow-226001
www.manyagroup.com