How do you add numbers 1 through 500?

The best trick for this is to think of averages. Put the 1 with 500, 2 with 499,, 3 with 488, ... On average these numbers are (1 + 500)/2 or 250.5 So you want to add up 500 numbers each of which is, on average 250.5 The answer is 500 x 250.5 which is 125250