# Handshake question

• Jun 22nd 2010, 03:47 AM
MathBooBoo
Handshake question
Hello (Hi),

There are 70 participants in a workshop, each and everyone of them shook hands with each other once. How many handshakes were done?

Thank you
• Jun 22nd 2010, 04:16 AM
CaptainBlack
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..

CB
• Jun 22nd 2010, 04:29 AM
MathBooBoo
Hi CaptainBlack,

I know where you are coming from, just need to know the equation needed.

Not wanting spoon feeding, just that I am really bad in mathematics with only bits and pieces knowledge.

Thank you
• Jun 22nd 2010, 05:47 AM
HallsofIvy
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.
• Jun 22nd 2010, 05:49 AM
Quote:

Originally Posted by MathBooBoo
Hi CaptainBlack,

I know where you are coming from, just need to know the equation needed.

Not wanting spoon feeding, just that I am really bad in mathematics with only bits and pieces knowledge.

Thank you

OR since a handshake involves 2 ppl, and there are 70 ppl in total, this is a process of selecting 2 different ppl from 70 so you can use combination.

$70 \choose 2$
• Jun 22nd 2010, 05:54 AM
CaptainBlack
Quote:

Originally Posted by MathBooBoo
Hi CaptainBlack,

I know where you are coming from, just need to know the equation needed.

Not wanting spoon feeding, just that I am really bad in mathematics with only bits and pieces knowledge.

Thank you

Mathematics (what ever you may have been told and/or taught) is not about knowing the formula for everything, its about solving problems. I and others have shown you how to solve this, and left enough of it for you to finish and with luck learn from. If we went any further we may as well have not wasted our time and just told you the answer, which strange as it may seem would have required less effort on our part than showing how you might go about solving such problems.

CB