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July 19th, 2009, 11:24 AM  #1 
Newbie Joined: Jul 2009 Posts: 1 Thanks: 0  Permutation or Combinations
I am having a hard time distinguishing which problem is a permutaion or combination. (1) In how many ways can the three fastest runners finish a race if there are 10 runners racing. (2) In how many distinct ways can the digits in the telephone number 7788665555 be arranged? 
July 20th, 2009, 03:28 PM  #2 
Newbie Joined: Feb 2009 Posts: 8 Thanks: 0  Re: Permutation or Combinations
(1)Combination (2)Premutation 
August 2nd, 2009, 12:54 PM  #3 
Member Joined: Jul 2009 Posts: 34 Thanks: 0  Re: Permutation or Combinations
They are both permutations, because in case of a combination, the order doesn't matter. And in both cases the order does matter. An example of a combination: How many distinct committees can you form out of 30 students? The order in such a committe doesn't matter. 
August 4th, 2009, 07:43 AM  #4 
Global Moderator Joined: Nov 2006 From: UTC 5 Posts: 16,046 Thanks: 938 Math Focus: Number theory, computational mathematics, combinatorics, FOM, symbolic logic, TCS, algorithms  Re: Permutation or Combinations
Jeranimo is quite correct here.


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