Sum of the counting numbers

Find the sum of the counting numbers  from 1 to 25 inclusive. In other words, if S=1+2+3+4....+24+25, find the value of S.

MetroEye: The sum of first n integers/counting numbers is S= n(n+1)/2

Here n = 25
So Sum S= 25(25+1)/2 = 325

Sum of the counting numbers from 1 to 25 is 325.