tricky courtesy
Level
pending
There are 10 men at a business meeting. Each one of them shakes his hand with every one. At each hand shake 2 courtesies are exchanged. What is the total number of courtesies exchanged.
The answer is 90.
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1 solution
1st man can shake hand with other 9 people. Similarly
2nd man can shake hand with other 8 people. Similarly
3rd man can shake hand with other 7 people. So on .......
9th man can shake hand with other 1 people.
10th man can shake hand with other 0 people.
Total handshake=0+1+2+ .......... +8+9=9x10/2=45(sum of n natural number)
So total courtesies exchange=45x2=90