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How is permutation different from combination?
Permutation Vs. Combination
- Thread starter lilietta2000
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Basically, in a permutation order matters and in combinations it does NOT. The formula for a permutation is as follows P = n! / (n-r)! whereas for combination it is C = n! / r!(n-r)!
Ex) If there are 10 senators chosen for groups of 3, how many diff groups of 3 would you have??
Ans) This would be a combination b/c order within the groups doesnt matter. So... 10 C 3 where n= 10 and r= 3. so formula would be C = 10! / 3! (10 - 3)!
If this is all still a bit confusing, maybe post a question and Ill walk you through it. Hope that helped
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Im usually pretty good at math, but this one has me stumped. it has been five years since i took AP stats back in high school, so maybe thats why i dont remember... anyway, in this case order clearly matters, so it would be a permutation. but its not as simple as just using the equation i posted earlier. since some of the items in the set are identical some of the answers would overlap for instance ... 6, 0', 0,1,0,1 would be same as 6,0,0',1,0,1 right???
STREETWOLF where are youuuuu???
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It's hard to give a good formula on a message board but the answer is:
6! / 3!2! = 60
The 6! sorts them in any order. The 3! removes the repeats caused by the 3 identical 0s. The 2! removes the repeats caused by the 2 identical 1s.
In general for this exact type of problem you would do the # of elements factorial in the numerator. In the denominator you want to have a bunch of factorials. Each factorial represents a unique element with a repeat. Of course you could list EVERY element but the ones that occur once would be 1! which equals 1 so that's pretty useless. For the ones that repeat, you count up the # of times they repeat and put that number factorial in the denominator.
Another example is to ask how many ways you can arrange the letters in the word MISSISSIPPI. There are 11 letters. The I repeats 4 times as does the S. The P repeats twice.
11! / 4!4!2! = 34,650. That's a lot of ways.
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Brilliant and thanks for the bonus example too, I remember seeing that MISS problem once upon a time! youre a Math BEAST!! PS if you read this again Mr. Streetwolf could i hit you up with a few math questions at some point in the next couple of weeks??? like i said, ive always been pretty good at math but havent taken it since freshman year. im consistently missing the same type of questions (in prob, trig, and geo). still im getting 21+ on topscore and crack dat math - dont know how realistic the scores are tho). if you could explain them i should be money for QR. 😀
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Yeah sure. Got one more big test Monday. After that I'm finally free of D1 and get 2 months off 🙂. That'd be a good time to ask questions.
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duly noted. thanks ahead of time street, the more i can fluff my DAT w/ QR the better haha. good luck with that test of yours!
