SOLUTION: How many permutations are there of 1,2,...,2n have every even number in an even-numbered position?

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Question 215180This question is from textbook Topics in Finite and Discrete Mathematics
: How many permutations are there of 1,2,...,2n have every even number in an even-numbered position? This question is from textbook Topics in Finite and Discrete Mathematics

Answer by Edwin McCravy(20055) About Me  (Show Source):
You can put this solution on YOUR website!
How many permutations are there of 1,2,...,2n have
every even number in an even-numbered position?


There are n even integers and n odd integers.



There are n%21 ways to place the even integers.

For every one of those ways, there are n%21 ways 

to place the odd integers.



That's  n%21%2An%21=n%21%5E2



Edwin