Permutations/Combinations

[osimsDDS]

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Can someone give me a quuiiickk run-down on permutations and combinations???

I always forget which one is about order and which is not..thanks!!!

 

[Thundercatz]

http://betterexplained.com/articles/easy-permutations-and-combinations/

This is the best explanation I have found, which really helped me out.

 

[osimsDDS]

sweet, so permutations order matters, combinations it does not but you have to get rid of redundencies...

So permutations: n!/(n!-k)
and Combinations: n!/r!(n!-r!)

correct me if iam wrong, thanks again

 

[Thundercatz]

Thats right! Actually, if you understand how the problem works, you dont even need to remember the forumla. Makes it even easier and faster IMO.

 

[Andrew324]

Yeah thats a great site, thanks for sharing it!

 

[DRHOYA]

While we are on this subject. Can someone explain the difference between Destroyer QR #'s 27 and 87. To me, they seem like the question is asking the same thing.........but for 27 they use nCr, and for 87 it is simply nPr?? Also, #86 uses nPr. Thanks.