I was chatting with my eight year old, asking him about his physical education lesson last week. He replied that they were learning how to bounce a basketball and he came up with a game. He would bounce once, then twice, then thrice, and so on but he only managed to get to eight consecutive bounces. We were walking towards the car, so I then asked him to find a piece of paper afterwards and add up the sum 1+2+ … + 8.
I was pleasantly surprised when he replied after a short while (we were still walking) that the answer was 55 -19 and after another pause, he worked out that 55 -19 =36.