Math Question

[AgaBoogaBoo]

Is there some way to remember difference or maybe a clear difference between permutations and combinations?

 

[Description]

Look it up?

 

[AgaBoogaBoo]

I did, but I'm not sure, it's not getting across to me real well

 

[Description]

The way I remember it:

Permutation
A rearrangement of the elements of a set.

Combination
One or more elements selected from a set without regard to the order of selection.

 

[AgaBoogaBoo]

Here's a problem: Four students are to be assigned to 4 different summer jobs. Each student is qualified for all 4 jobs. In how many ways can the jobs be assigned?

Answer is 24.

That means permutation was used, why not combination? Order doesn't matter in this case

 

[suklee]

Yuck, Combinatorics.
Sorry can't help you, I've forgotten all C&O stuff I learn... err, memorized last year.

 

[Description]

4!

4^4

 

[AgaBoogaBoo]

But what's the resasoning?

 

[esun]

Permutations

Combinations

 

[cronos]

let's say there are four items: A, B, C, and D.
you have to make a set of two items.

in permutation: AB = BA, permutation regards it as a same set (the order does not matter)
in combination AB != BA, combination regards it as a different set (the order matters)

 

[mAdD INDIAN]

Originally posted by: AgaBooga
Here's a problem: Four students are to be assigned to 4 different summer jobs. Each student is qualified for all 4 jobs. In how many ways can the jobs be assigned?

Answer is 24.

That means permutation was used, why not combination? Order doesn't matter in this case

it's permutation because order matters.

You have four different jobs one student can have right? Once the first student gets a job, you have three students left with three different jobs. So now each student has three different ways. Then second student gets a job, so now two students have two remaining jobs. This means each student has two ways to get a job. Then third guy gets job, so one student left with one way to get the job.

that comes out to 4 ways to get job x 3 ways to get job x 2 ways to get job x 1 way to get job = 4x3x2x1 = 24 ways.

Order matters because once one student gets a job, there are fewer jobs to get.

Hope that helps.

 

[AgaBoogaBoo]

Thanks everyone! :beer: