I've forgotten how to do this type of question? Question below...

Find an expression for the total number of handshakes needed if #n# people all shake hands with each other.

1 Answer



Note that this explanation might be confusing.

Let's say three people shook hands with each other. Their names are A, B, C, and D.
A: B, C, D
B: A, C, D
C: A, B, D
D: A, B, C

Some are counted more than once. Cross them out.
A: B, C, D
B: C, D
C: D
That is #1+2+3=6#. Try this with other problems.