for any positive integer n , the sum of the first n positive integers equals n ( n + 1 ) / 2 . what is the sum of all the integers between 1 and 50 ?
"sum = 50 * 51 / 2 = 25 * 51 = 1275 answer is a"
add(divide(subtract(subtract(50, 1), add(1, 1)), 2), 1)