Summation by folding

The sum of 1 to 100 is classically found by pairing the ends to make 101. This note offers a different way to see it: lift the four corners of a ten-by-ten grid of 1 to 100 into a cone-like shape. Lines of the grid then fold onto themselves like meridians, each number meeting its partner at 101, for 50 pairs and a total of 5050. The result is standard; only the picture is new