Permutations and Computations

[edkNARF]

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1st-What is the differnce between the two?
2nd-How do you know the differnce between the two in QR problems?
3rd-How do you do the problems?
Thanks.

 

[combinator]

i dont even know what hose words mean and i got a 22 on my dat qr section

 

[HBomb]

combinator, nice score. Good for you.

edk, you use permutations when order matters. You use combinations when order doesn't matter. For instance, how many ways are there to pick 2 number from a list of 1,2,3,4,5. If order matters (like {2,4} is different than {4,2}) then use permutations. If order doesn't matter (so if you pick a 2 and 4 in any order), then use combinations. Maybe this makes more sense: How many ways to choose a batting order (9 people) from a team of 25? You would have to use permutations. For combinations: how many ways to choose 3 groomsmen from a group of 8 friends?

The mathematical formula for a permutation is: P(n,k) = n!/(n-k)! = P(25,9) = 25!/16!
The mathematical formula for a combination is C(n,k) = n!/k!(n-k)! = C(8,3) = 8!/(3!5!)

I also found good stuff on the web:
http://mathworld.wolfram.com/Permutation.html
http://mathworld.wolfram.com/Combination.html

 

[combinator]

combinator, nice score. Good for you.

edk, you use permutations when order matters. You use combinations when order doesn't matter. For instance, how many ways are there to pick 2 number from a list of 1,2,3,4,5. If order matters (like {2,4} is different than {4,2}) then use permutations. If order doesn't matter (so if you pick a 2 and 4 in any order), then use combinations. Maybe this makes more sense: How many ways to choose a batting order (9 people) from a team of 25? You would have to use permutations. For combinations: how many ways to choose 3 groomsmen from a group of 8 friends?

The mathematical formula for a permutation is: P(n,k) = n!/(n-k)! = P(25,9) = 25!/16!
The mathematical formula for a combination is C(n,k) = n!/k!(n-k)! = C(8,3) = 8!/(3!5!)

I also found good stuff on the web:
http://mathworld.wolfram.com/Permutation.html
http://mathworld.wolfram.com/Combination.html

I really think people overrate this section on the DAT. IMHO, I believe 'most' people who do well on the qr portion have a solid math background.