BREAKING: Target Test Prep releases Brand New 2026 On Demand GMAT prep course

Redeem

Combination Permutation Strategy

This topic has expert replies
Post new topic Post Reply
Previous Topic Next Topic
Senior | Next Rank: 100 Posts
Posts: 67
Joined: Mon May 03, 2010 12:03 pm
Thanked: 3 times

Combination Permutation Strategy

by myfish » Fri Apr 27, 2012 11:21 am
I understand that the Combination and Permutation-formula can be used interchangeably as they are essentially the same. However, I stumble repeatedly over one type of question where I am not sure which question I should be using.

Example 1:
If there are 2 empty chairs left in an auditorium but there are 8 people who need to be seated, in how many number of different ways can those 8 people be seated on 2 empty chairs?

Example 2:
How many different ways are there to choose 2 candidates from 8 possible candidates?

Both questions deal with 8 into 2. However, one is done via Permutation and one is Combination! WHY? How can i identify which one to use, without guessing?

Thanks a lot to all the geniuses out there that can answer this sufficiently.
Top
Source: — Problem Solving |
User avatar
Senior | Next Rank: 100 Posts
Posts: 30
Joined: Tue Dec 20, 2011 2:11 pm
Thanked: 4 times
Followed by:1 members

by Lasve » Fri Apr 27, 2012 1:58 pm
I use a simple Trick:
PERMUTATION = Position count, that means that if we have to "permutate" threee people (A;B;C) it is differetn wheter we have ABC or BCA so ABC ≠ BCA


COMBINATION = Position does NOT count, that means that if you have to "combine" three people (A;B;C)
Wether you have ABC or BCA is actually THE SAME!

Combination is a sort of IN or OUT Question
Permutation not only wants to know WHO seated, but also in What order!

Hope I helped to clarify your problem a little!
Top
User avatar
Senior | Next Rank: 100 Posts
Posts: 30
Joined: Tue Dec 20, 2011 2:11 pm
Thanked: 4 times
Followed by:1 members

by Lasve » Fri Apr 27, 2012 1:58 pm
I use a simple Trick:
PERMUTATION = Position count, that means that if we have to "permutate" threee people (A;B;C) it is differetn wheter we have ABC or BCA so ABC ≠ BCA


COMBINATION = Position does NOT count, that means that if you have to "combine" three people (A;B;C)
Wether you have ABC or BCA is actually THE SAME!

Combination is a sort of IN or OUT Question
Permutation not only wants to know WHO seated, but also in What order!

Hope I helped to clarify your problem a little!
Top
User avatar
Master | Next Rank: 500 Posts
Posts: 134
Joined: Fri Apr 06, 2012 3:11 am
Thanked: 35 times
Followed by:5 members

by Shalabh's Quants » Sat Apr 28, 2012 5:46 am
myfish wrote:I understand that the Combination and Permutation-formula can be used interchangeably as they are essentially the same. However, I stumble repeatedly over one type of question where I am not sure which question I should be using.

Example 1:
If there are 2 empty chairs left in an auditorium but there are 8 people who need to be seated, in how many number of different ways can those 8 people be seated on 2 empty chairs?

Example 2:
How many different ways are there to choose 2 candidates from 8 possible candidates?

Both questions deal with 8 into 2. However, one is done via Permutation and one is Combination! WHY? How can i identify which one to use, without guessing?

Thanks a lot to all the geniuses out there that can answer this sufficiently.
Thumb Rule-- Whenever Qn. uses words like Arrangement, Distinct, Unique. One must calculate Permutation & when Qn. uses words like Selection, Choose, calculate combination.
Shalabh Jain,
e-GMAT Instructor
Top
Post new topic Post Reply
• Page 1 of 1