What's the difference between Permutations and Combinations? (1 Viewer)

[cranberries]

I cannot understand the difference! Well, I do sort of, like I read the definitions and it says P are ordered selections and C are unordered. But I never know when to use them, because I don't really understand what they mean

Can anyone help? Like, when it's dice or cards or seating- how do you know which to use?

 

[Xayma]

Permutations order matters.

For example if you want to know how many ways can people line up then you have a permutation because Bill, Jane, Fred is different from Jane, Fred, Bill.

Combinations order doesn't matter.

For example a committe of Bill, Fred and Jane is the same as a committe of Jane, Fred and Bill.

 

[dawso]

yup, as xayma said, perms are wen order matters such as the number of arrangments of letters from a word, whereas combinations are commitee style questions, the lame but affective way our teacher tought us to tell the difference is that "wen ya go 2 the hairdressers, u gotta order if ya wanna buy a comb, u dont", lame, but affective, gud luck
-dawso

 

[Slidey]

Is that meant to be something like "If you want a perm at the hairdressers, you have to order, fi you want a comb, you don't"? It took me about a minute to make sense of it.

Personally I think remembering "permutation=ordered, combination=unordered"

Also, a combination is the permutation on r!, or (n!/(n-r)!)/r!, which is n!/[r!(n-r)!].

Um. Here is a lame example: I recently made a poll in the School forum which had options in groups of two universities. Eg: a is a univeristy, B is another: one option was AB. Now, there are 23 universities in Australia, I think, and we are taking them TWO at a time. The amount of possible permutations is then 23^P_2, or 23!/(23-2)!=22*23=506. HOWEVER, order doesn't matter. Here, the combination (uni A, uni B) is exactly the same as the combination (uni B, uni A). So we must divide our number of permutations by r!, which is 2!, or 2. Thus the answer is 253.

We could skip the permutation step and do this: 23^C_2,
23!/(2*21!)=23*22/2=11*23=253.

Sorry. I did that ebcause I think comittee and people questions are boring.

 

[hipsta_jess]

This is just repeating what the others have said, but it helped me to remember which was which.
permutations- order is important
combinations- you don't give a crap about order

 

[dawso]

yes slide rule, thats wat i meant, lol, my bad, i just read wat i said and it makes no sense, thats wat ya get wen ur chattin on msn and tryin 2 write up a post at the same time, oh well, hope this post makes sense, u all got the message anyway
-dawso

 

[cranberries]

wow! thanks guys, that actually helped!!

I get it now- your explantation was great slide! much better than the committees

 

[jumb]

This is just repeating what the others have said, but it helped me to remember which was which.
permutations- order is important
combinations- you don't give a crap about order

Perm/Comb in general are crap

 

[Shuter]

Is it really that hard to remember: Permutation = order, Combination = unordered. I didn't think it needed ryhmes to help you remember. I mean it's 4 terms, even a monkey can remember 4 terms.*




*May not be a true statistic.

 

[withoutaface]

Yeah but when you combine that with other stuff you need to know, and multiply that by a few subjects, it gets a bit tricky for some people...