what is the average ( arithmetic mean ) of the numbers 16 , 17 , 17 , 18 , 19 , 19 and 20 ?
"{ 16 , 17 , 17 , 18 , 19 , 19 , 20 } = { 18 - 2,18 - 1,18 - 1 , 18 , 18 + 1 , 18 + 1,18 + 2 } - - > the average = 18 . answer : a ."
divide(divide(multiply(add(16, 17), add(divide(subtract(17, 16), 16), const_1)), const_2), add(divide(subtract(17, 16), 16), const_1))