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If I have 5 letters (A,B,C,D,E), and I want to form groups of three letters.
a) How many can I form? (AAA, AAB, AAC, etc)
b) How many without repeating? (ABC, ABD, etc)
 5 months ago
 5 months ago
If I have 5 letters (A,B,C,D,E), and I want to form groups of three letters. a) How many can I form? (AAA, AAB, AAC, etc) b) How many without repeating? (ABC, ABD, etc)
 5 months ago
 5 months ago

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Easyaspi314Best ResponseYou've already chosen the best response.0
a) thats a combination of 3 from 5..or 5 C 3
 5 months ago

osansevieroBest ResponseYou've already chosen the best response.0
So 125 in the first one, and 20 in the second one. Why is it n(n1)?
 5 months ago

HeroBest ResponseYou've already chosen the best response.1
If I'm not mistaken the first one is a permutation since elements are allowed to repeat. Which means the total number of three letter formations should be \(n^r=5^3 = 125\) The second question is a combination since elements are not allowed to repeat. So I imagine that it is \(5C3\)
 5 months ago

osansevieroBest ResponseYou've already chosen the best response.0
Ok, let me check :)
 5 months ago

osansevieroBest ResponseYou've already chosen the best response.0
I searched an in a permutation elements cant be repeated :/
 5 months ago

HeroBest ResponseYou've already chosen the best response.1
You should do more research on permutations.
 5 months ago

osansevieroBest ResponseYou've already chosen the best response.0
So the basic formulas are \[n ^{r}\] if they can be repeated and NCr, when they cant be repeated?
 5 months ago

HeroBest ResponseYou've already chosen the best response.1
This resource might help clear things up a bit more: http://www.mathsisfun.com/combinatorics/combinationspermutations.html
 5 months ago

osansevieroBest ResponseYou've already chosen the best response.0
Yep, this helped me a lot :)
 5 months ago

osansevieroBest ResponseYou've already chosen the best response.0
I am seeing that the formula of the combinations without repetition and permutation without repetition are the same. How can I know if this if a permutation or a combination? (the order matters here?)
 5 months ago

osansevieroBest ResponseYou've already chosen the best response.0
oops, not the same, I reduce by r one more time. But how can I know in this case if it is permutation or combination?
 5 months ago

osansevieroBest ResponseYou've already chosen the best response.0
(from the question?, how can I know if order matters?
 5 months ago

osansevieroBest ResponseYou've already chosen the best response.0
So it is 125 and 10 :)
 5 months ago
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