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 one year 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)
 one year 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)

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Easyaspi314
 one year ago
Best ResponseYou've already chosen the best response.0a) thats a combination of 3 from 5..or 5 C 3

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

Hero
 one year ago
Best ResponseYou've already chosen the best response.1If 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 \(5C3\)

osanseviero
 one year ago
Best ResponseYou've already chosen the best response.0Ok, let me check :)

osanseviero
 one year ago
Best ResponseYou've already chosen the best response.0I searched an in a permutation elements cant be repeated :/

Hero
 one year ago
Best ResponseYou've already chosen the best response.1You should do more research on permutations.

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

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

osanseviero
 one year ago
Best ResponseYou've already chosen the best response.0Yep, this helped me a lot :)

osanseviero
 one year ago
Best ResponseYou've already chosen the best response.0I 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?)

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

osanseviero
 one year ago
Best ResponseYou've already chosen the best response.0(from the question?, how can I know if order matters?

osanseviero
 one year ago
Best ResponseYou've already chosen the best response.0So it is 125 and 10 :)
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