My Math Forum Help on Combinatorics

 Probability and Statistics Basic Probability and Statistics Math Forum

 January 29th, 2017, 07:44 AM #1 Senior Member   Joined: Jan 2016 From: Blackpool Posts: 104 Thanks: 2 Help on Combinatorics Hey guys I am struggling to understand what the difference is between ordered and unordered selection between a set of elements. Could anyone please give me an example which i might find helpful to understand them? Thanks again and sorry for the spam!
January 29th, 2017, 08:42 AM   #2
Senior Member

Joined: Sep 2015
From: USA

Posts: 2,452
Thanks: 1337

Quote:
 Originally Posted by Jaket1 Hey guys I am struggling to understand what the difference is between ordered and unordered selection between a set of elements. Could anyone please give me an example which i might find helpful to understand them? Thanks again and sorry for the spam!
Consider selecting colored balls from an urn as in your other problem.

The set will be ordered if I care about which color was selected first, which was selected second, etc.

In this case, $\{B, B, G\}$ is considered a distinct event from $\{G, B, B\}$

On the other hand if we only care about what balls we end up with after all the selections are made we have an unordered selection.

In this case the two color triples above are considered the same event.

Last edited by romsek; January 29th, 2017 at 09:36 AM.

January 29th, 2017, 05:07 PM   #3
Senior Member

Joined: Feb 2010

Posts: 706
Thanks: 141

Quote:
 Originally Posted by Jaket1 Hey guys I am struggling to understand what the difference is between ordered and unordered selection between a set of elements. Could anyone please give me an example which i might find helpful to understand them? Thanks again and sorry for the spam!
Suppose we have three people Al (A), Bob (B), and Chuck (C). Now consider the set of people $\displaystyle \{A,B,C\}$.

1. Suppose we want to know how many committees of size 2 can be formed. There are 3. They are AB, AC, and BC. Notice that if the committee is Al and Bob, then Bob and Al is the same committee.

2. Suppose we want to know how many president, vice-president pairs there are. There are 6. They are AB, BA, AC, CA, BC, CB. Notice that president Al and vice-president Bob is different than president Bob and vice-president Al.

The first problem is called a combination. The second is called a permutation.

 Thread Tools Display Modes Linear Mode

 Similar Threads Thread Thread Starter Forum Replies Last Post Gamegeck Applied Math 3 May 22nd, 2014 11:15 PM orangestripes Number Theory 0 March 30th, 2014 10:01 AM yo79 Math Events 6 February 6th, 2013 01:48 AM proglote Algebra 4 September 8th, 2011 07:19 AM proglote Algebra 4 August 9th, 2011 02:34 AM

 Contact - Home - Forums - Cryptocurrency Forum - Top