Question
Please help-I'm really mixed up
How do I find the permutations of the first 12 letters taken 3 at a time?
I have a ton of these to do and really don't understand them at all-
How do I find the permutations of the first 12 letters taken 3 at a time?
I have a ton of these to do and really don't understand them at all-
Answers
Damon
permutations:
That means all the arrangements of three made from the 12 when order is important. For example
ABC and ACB and BAC and BCA and CAB and CBA are all different.
The formula for that is
n!/[n-r]!
here n = 12 and r = 3
so we have
12!/9! which is 12*11*10 = 132
That is what you asked.
To answer what is coming next, combinations of n taken r at a time where order is NOT important are called indeed combinations and the formula is logically enough the permutation formula divided by r!
C(n,r) = n!/[ r! (n-r)! ]
That means all the arrangements of three made from the 12 when order is important. For example
ABC and ACB and BAC and BCA and CAB and CBA are all different.
The formula for that is
n!/[n-r]!
here n = 12 and r = 3
so we have
12!/9! which is 12*11*10 = 132
That is what you asked.
To answer what is coming next, combinations of n taken r at a time where order is NOT important are called indeed combinations and the formula is logically enough the permutation formula divided by r!
C(n,r) = n!/[ r! (n-r)! ]
Anna
Thank you for the explanation-it actually makes sense now