Swantatratagaamy (phew!)...You make sense. "They sell all their cows - each cow gets sold for an amount that is equal to the total number of cows they had, .." Here is how I interpreted the above sentence by which I got the total initial sum to be (x^2+x)/2. Let's say they started with x cows. The first cow is sold at $x. Then they are left with (x-1) cows. The second cow is sold at $(x-1), and so on and on. No of cows left Amount recieved x x x-1 x -1 x-2 x-2 x-3 x-3 . . . . . . x - (x-2) x-(x-2) x-(x-1) x- (x-1) So, if you sum up the second column, you get (x^2+x)/2. May be I was reading in "too much" but that's the way I interpreted what that sentence meant. Anyway, keep these coming!