Yes, there is.
Now, let n=100
Question:
Suppose you have a list of numbers from zero to one hundred. How quickly can you add them all up without using a calculator?
Is there a simple way or a trick to add them quickly?
100 + 1 = ?
99 + 2 = ?
98 + 3 = ?
...
51 + 50 = ?
How many such pairs are there?
So what is the sum?
See also this thread