bleak flare
In 4 permutations, the first 2 letters can be the same but the last 2 letters are different, and it is counted as a permutation (ABCD, ABDC). The first two (AB) are the same, and the last two (CD and DC) are in different arrangements, still counted as two permutations. That’s why we have to subtract it with the selected value, which is 2
Is this correct?
quick rootBOT
bleak flare
Since it only needs 2, ABCD and ABDC will be AB AB, which is duplicate
N = 4
R = 2
I forgo
quick rootBOT
Please show the original problem, exactly as it was stated to you, with the entire original context. A picture or screenshot is best. If the original problem is not in English, then post it anyway! The additional context might still be helpful. Do your best to provide a translation.
bleak flare
It is not clear to me what you are trying to accomplish.
All permutations of ABCD
If selected is only 2 (R = 2) It is noticeable that there are duplicates so that's why it needs to be divided by N - R
Resulting this only 12
I just need confirmation
zealous wolf
nPr = n!/(n-r)!
Are you familiar with this?
It is the number of permutations of n elements considering only the first r elements of the permutation.
For you, you have 4P2 = 4!/(4-2)! = 24/2 = 12
The fact that each permutation pair ABCD, ABDC has two options for the last two elements is captured by the fact that 2! = 2.
Does this make sense? @bleak flare
bleak flare
nPr = n!/(n-r)!
Are you familiar with this?
Yes, I am just trying to visualize why it need to be subtracted by r
bleak flare
If selected is only 2 (R = 2) It is noticeable that there are duplicates so that...
@zealous wolf you can see in the 2nd image
zealous wolf
Because if you select r, then you do not select n-r. And the order that those n-r elements can be in is (n-r)!
bleak flare
Because if you select r, then you do not select n-r. And the order that those n-...
yes it is (n-r)!
But is my visualization correct? like in 4! which is all possible permutation of ABCD, the first 2 letters are the same, so by (n - 2)! removing half of it
catch my drift? I am bad at explaining sorry
zealous wolf
I mean, sure it's not wrong. However, that visualization might be difficult to extend to (for instance) even mildly small examples such as 9P5
bleak flare
I mean, sure it's not wrong. However, that visualization might be difficult to e...
I see
It doesn't even need to fully visualize it tbh, that's a lot of permutation to think about