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 even integers between 99 and 201 ?
"100 + 102 + . . . + 200 = 100 * 51 + ( 2 + 4 + . . . + 100 ) = 100 * 51 + 2 * ( 1 + 2 + . . . + 50 ) = 100 * 51 + 2 ( 50 ) ( 51 ) / 2 = 100 * 51 + 50 * 51 = 150 ( 51 ) = 7650 the answer is a ."
add(divide(subtract(subtract(201, 1), add(99, 1)), 2), 1)