Math - Permutations and Combinations: Did you guys ever get it?

[tom_mai78101]

In our country, we learn permutations and combinations in the second semester of our freshman high school years. I don't know about the rest of the countries, so I'm guessing you guys learn these in college, since permutations and combinations are re-discussed in statistics. (College junior years, 2nd semester)

Any of you recalling the memories of getting started in these math subjects know how to fully grasp the usage of these? My little brother is studying these for his first exam of the upcoming spring semester (which starts on the second to third day of school), he asked me some of the problems, and I just couldn't make it through one problem.

Any of you still remembers how permutations and combinations works?

 

[KaerfNomekop]

Me. I'll have the stuff in my head until this June at least.

 

[Accname]

I have had to learn this stuff for first semester of computer science.
But i dont think i could help you in english, i only know the technical terms in my native language.

 

[Dave312]

From memory, Permutations just calculates how many different possible ways you can select X values from a pool of Y possible values. Combinations essentially calculates the same thing but the order in which each object is selected does not matter. For example if I have 5 jelly beans of different colours and I choose 5 jelly beans to eat, in the end I will eat all the jelly beans so there is only 1 outcome (Combination, 5 nCr 5 = 1). If however I want to look at the order I eat the jelly beans, then there would be 120 different outcomes (Permutation, 5 nPr 5 = 120). Hope that makes sense

 

[XXXconanXXX]

I'm guessing you mean set permutations and combinatorial analysis. Combinatorics goes far deeper than just statistics and basic math - it's use is seen in differential calculus, linear algebra, typed lambda calculus, and set theory (Obviously). Number of combinations can be infinite given 2 inputs or more, and the permutations of the set can be countable if the set itself is countably infinite. It really depends on the context in which you use those two terms, which in this case is extremely vague.

 

[tom_mai78101]

Looks like I just swept the surface of my statistics book.

 

[thewrongvine]

Uh, I also learned this stuff throughout high school I believe. I think I would get it/remember it when I needed to for exams but it's not something I am adept at.

 

[camelCase]

Meh, I only use it on occasion. Like, I play "Pump it Up!" (DDR with five arrows) and a little thought experiment I did in my head was calculating the amount of valid two-note combinations assuming double-stepping and turns are not allowed.

And.. A few other times but I don't quite remember.. But knowing this stuff is kinda' useful every now and then, I guess.

Edit:
Also, whoops. Necro'd this from about a month ago.