Less than Relation

Oct 2009
255
20
St. Louis Area
The less-than relation on [4] is the set
R={(1,2),(1,3),(1,4),(2,3),(2,4),(3,4)}

In other words, (a,b) \(\displaystyle \in\) R if and only if a < b. It contains six ordered pairs.

How many ordered pairs are in the less-than relation on [n]?

How many are in the less-than-or-equal-to relation on [n]?

The answer to the first question is \(\displaystyle \sum_{i=1}^{n-1}i\) or \(\displaystyle \left({n\atop 2}\right)\).

I come up with the following for the second quesiton \(\displaystyle \sum_{i=1}^{n}i\) or \(\displaystyle \left({{n+1}\atop 2}\right)\). Correct?
 
Oct 2009
255
20
St. Louis Area
Yes, that is correct.
Thanks for all your help. I realize my hillbilly math is a little crude sometimes, but I'll try to clean it up after my classes start and I have access to my professor.