## Dhaka Higher Secondary 2010/7

Problem for Higher Secondary Group from Divisional Mathematical Olympiad will be solved here.
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Please don't post problems (by starting a topic) in the "Higher Secondary: Solved" forum. This forum is only for showcasing the problems for the convenience of the users. You can post the problems in the main Divisional Math Olympiad forum. Later we shall move that topic with proper formatting, and post in the resource section.
BdMO
Posts: 134
Joined: Tue Jan 18, 2011 1:31 pm

### Dhaka Higher Secondary 2010/7

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?

leonardo shawon
Posts: 169
Joined: Sat Jan 01, 2011 4:59 pm
Location: Dhaka

### Re: Dhaka Higher Secondary 2010/7

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
Posts: 158
Joined: Wed Dec 08, 2010 5:36 pm

### Re: Dhaka Higher Secondary 2010/7

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

HandaramTheGreat
Posts: 135
Joined: Thu Dec 09, 2010 12:10 pm

### Re: Dhaka Higher Secondary 2010/7

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\$...

kamrul2010
Posts: 120
Joined: Wed Dec 08, 2010 2:35 am
Contact:

### Re: Dhaka Higher Secondary 2010/7

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?

leonardo shawon
Posts: 169
Joined: Sat Jan 01, 2011 4:59 pm
Location: Dhaka

### Re: Dhaka Higher Secondary 2010/7

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

long way to go .....