Rangpur Secondary 2011/9

Problem for Secondary Group from Divisional Mathematical Olympiad will be solved here.
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Rangpur Secondary 2011/9

Unread post by Moon » Wed Feb 02, 2011 6:50 pm

Problem 9:
At a convention, flags of $4$ countries are to be hoisted on $2$ poles so that no pole is left empty and all the flags get hoisted. More than one flag must not be placed at the same height of the same pole. Rather, they can be placed above or below an already placed flag. In this manner, more than one flag can be placed serially on a single pole. How many ways can the flags be hoisted?
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Tahmid Hasan
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Re: Rangpur Secondary 2011/9

Unread post by Tahmid Hasan » Wed Feb 02, 2011 8:05 pm

the possible cases are 2 flags o each pole,3 on first and3 on 2nd.
in each of the cases the flags can be hoisted in $4!$ ways. so the ans is $4!*3=72$
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