thanks for your reply.. It's the second part I just can't seem to get because if you choose 3 out of 12 and you only have 3 spots that can be filled.. Why is it a combination because if either of those 12 take a seat in the delegation then only 11 can still be seated next to the other one eventually leading to 12!/9!
If the 3 are duplicates, why, for example if you have 3 chairs and 7 people, that is not a duplicate.. Either way it also wouldnt matter who sits on what chair out of the 3 people that eventually will take a seat.. But, because if one person takes a seat on the first chair then there are only 2 chair left for 6 people etc. etc.
I think my main problem is that I just can't seem to get the difference behind the logic of these kind of questions.. Most of the time practicing, I end up thinking its a permutation while its a combination
I agree with gmat1220.
Arrangement and Order matters.
Let me give you a small example.
How many words can you form with two letters A and B, if the letters can't be repeated.
2 i.e. 2P2 = 2!(Permutation)
How many teams of 2 can you select with two girls A and B.
Can it be
No... AB and BA are both same teams. Order doesn't matter. If AB are used, that should be it.
The answer is 1.
2C2 = 1(Combination)
I don't get these concepts many times myself. Tell you my trick; I have by heart most of the patterns used in the combinations and permutations. Consequence: when I encounter a really witty question, I just scratch my head and roll my eyes. Then again, not many of the questions are witty.
Say for the above question, I would blindly solve it using combination. I won't even bother to look for alternative approaches. I know there are x people, y needs to be selected: ah.. selected(Combination). I got you Mr question.
3 out of 12 AND 2 out of 11
12C3 * 11C2 (I read it somewhere: AND is multiplication and OR is addition)
If you start with the pattern recognition in these questions like a robot, you will do just fine initially. The interesting part is: after solving many questions, you will automatically start getting the underlying logic behind the solution. Don't ask me how; just try it yourself. But, if you are a guy who just abhors to solve a question without proper visualization; please ignore my suggestion.
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