Question 449260
<pre>
How about the sequence of integers from 1 through 99.

1, 2, 3, ... , 97, 98, 99

To sum this sequence, let that sum be S,

 S =   1 +   2 +   3 + ... +  97 +  98 +  99

Then write the same sum in reverse order underneath it,
and add the two equations:

 S =   1 +   2 +   3 + ... +  97 +  98 +  99
 S =  99 +  98    97 + ... +   3 +   2 +   1 
--------------------------------------------
2S = 100 + 100 + 100 + ... + 100 + 100 + 100
2S = 99*100
2S = 9900
 S = 4950

So the sum of the integers from 1 through 99 is 4950.

Edwin</pre>