Please advise on the following :
There are 70 participants in a workshop, each and everyone of them shook hands with each other once. How many handshakes were done?
The first player shook hands 69 times
The second 69 times less the shake with the first player = 68 times
The third 69 times less the two with the first and second=67 times
the 68th player shook 69 times less 67 times already counted =1
All the skakes of the 69th player are alredy counted
So the total is?
..and this is not the only way of doing this..
Giving the formula would be "spoon feeding". The whole point of this problem is to think mathematically and derive the formula for yourself.
Here is another way, as Mr. Fantastic mentioned:
If there are a total of N people, each person shakes hands with each of the other N-1 people. That would give a total of N time N-1 handshakes, but each handshake counts for two people so that is twice as large as the actual number of handshakes.