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osanseviero
 3 years 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)
osanseviero
 3 years 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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anonymous
 3 years ago
Best ResponseYou've already chosen the best response.0a) thats a combination of 3 from 5..or 5 C 3

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

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

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

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

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

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