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Q&A #3398


Permutations and counting arrangements

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From: Claudia (for Teacher2Teacher Service)
Date: Apr 02, 2000 at 22:05:17
Subject: Re: Permutations and counting arrangements

I can't think of a "catchy" way, but basically, permutations deal with arrangements. I usually have my students draw little lines to represent how many things I am arranging. For example, if the problem says how many ways can a family of five be seated in a row for a picture? I have my students make five blanks ___ ___ ___ ___ ___ Then I go blank by blank and ask how many choices do I have...for the first blank? 5 Second blank....since people can't be repeated there are 4 choices left then 3 then 2 then 1 so the answer is 5 X 4 X 3 X 2 X 1 = 120 ways Now suppose my mom and dad had to sit on the ends??? ___ ___ ___ ___ ___ the first seat now only has 2 choices (mom or dad) the second seat has only 3 choices (one of the kids) work down...it looks like 2 X 3 X 2 X 1 X 1 = 12 ways (the last seat is a one because if mom or dad sat in the first seat, it leaves only one person left) Hope this helps -Claudia, for the Teacher2Teacher service

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