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#1 Re: Help Me ! » Combinations and Permutations » 2008-10-14 06:10:17

Thank you so much!  Thinking in terms of order and no order was completely throwing me off.

#2 Help Me ! » Combinations and Permutations » 2008-10-13 15:23:23

bbcnyc
Replies: 3

I keep doubting myself that I am calculating the following problem incorrectly:

How many sequences of three letters can be made from the letters {A, B, C, D, E} if

(a) The letters must be all different.

I would assume that I would use the permutation equation to solve this.  Pn,r = n!/(n-r)!

(b)  Repetitions are allowed.

I would assume I would use the combination equation to solve this.  Cn,r = n!/r!(n-r)!

If anyone can verify whether that is correct or incorrect I would greatly appreciate it.  Thanks!

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