permutations and combinations
Message posted by Danielle on March 28, 2000 at 12:00 AM (ET)

Can anybody come up with an easy explanation as how to recognize the difference between permutations and combinations? Use the following example: My home has a library with 50 different books (18 English, 17 French, and 15 Spanish) 1) How many ways can 2 be selected? Is it P(50,2) or C(50,2)? 2)How many ways can 3 be selected so there is 1 book from each language? Is it P(50,3) or C(50,3)? 3)How many ways can 3 be selected where one language is missing? I think this answer is a little more involved.

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Re: permutations and combinations
Message posted by Phil Rosenkrantz on March 28, 2000 at 12:00 AM (ET)

#1 can be permutation or combination depending on whether the order chosen is important. If order is a consideration, then you want permutation. If not, then you want combinations. Generally worded the way it is, combinations are what are being referred to.

#2 is a "multinomial" distribution problem which is based on combinations. You can find that in almost any probability and statistics book.

#3 is an "inclusion-exclusion" probability problem. You are right, they can get difficult. Refer to a probability & statistics text that was written for statistics majors.