Probability formula help please

[jac213]

I'm stuck on this problem. I think I need to come up with a formula here:

A company's network has n computers. All communications within the network have to be encrypted. Assuming each pair of computers needs one key for encryption, how many keys will have to be distributed by a company's Key Distribution Center if all keys have to be different?

 

[galactus]

Unless I am misunderstanding, it appears to be the number of ways of choosing 2 from n.

\(\displaystyle \binom n 2=\frac{n(n-1)}{2}\)