Dhaka Higher Secondary 2010/7

Problem for Higher Secondary Group from Divisional Mathematical Olympiad will be solved here.
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BdMO
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Dhaka Higher Secondary 2010/7

Unread post by BdMO » Tue Jan 18, 2011 2:05 pm

Boomboom joined Scout Jamboree. Every scout was said to handshake with each other. Some of them did not do. The total number of handshakes was $7$. Find the minimum number of handshakes which were not done?

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leonardo shawon
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Location:Dhaka

Re: Dhaka Higher Secondary 2010/7

Unread post by leonardo shawon » Tue Jan 18, 2011 6:42 pm

sorry wrong.... there will be 3
Last edited by leonardo shawon on Thu Jan 20, 2011 11:25 am, edited 2 times in total.
Ibtehaz Shawon
BRAC University.

long way to go .....

Dipan
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Re: Dhaka Higher Secondary 2010/7

Unread post by Dipan » Thu Jan 20, 2011 9:26 am

leonardo shawon wrote:ammm,, is the answer 1? Or 2. Im not sure.
proof????

HandaramTheGreat
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Re: Dhaka Higher Secondary 2010/7

Unread post by HandaramTheGreat » Thu Jan 20, 2011 11:10 am

if there is $n$ scouts then the number of handshakes is $\binom{n}{2}$, if all scouts do it...
as you are to find minimum number of handshakes which were not done, just find minimum value of $n$ such that $\binom{n}{2}$ is greater than $7$...
$\binom{5}{2}=10$

ans is $3$... :D

kamrul2010
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Re: Dhaka Higher Secondary 2010/7

Unread post by kamrul2010 » Sun Jan 30, 2011 9:26 am

I think question statement should be a little bit refined.

The part "Every scout was said to handshake with each other. Some of them did not do." should be replaced by something like "Every scout was said to handshake with each other. But some of them didn't handshake with all."

I first considered something like this, let $x$ be the number of total scout, & $y$ be the number of scout who didn't shake there hand with anyone...(blah blah blah)
If computers have no doors or fences, who needs Windows and Gates?

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leonardo shawon
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Re: Dhaka Higher Secondary 2010/7

Unread post by leonardo shawon » Sun Jan 30, 2011 11:18 am

i once try to figure it out with subset...
Ibtehaz Shawon
BRAC University.

long way to go .....

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