how many numbers from 10 to 1000 are exactly divisible by 9 ?
"10 / 9 = 1 and 1000 / 9 = 111 = = > 111 - 1 = 100 . therefore 100 answer : a"
add(divide(subtract(multiply(floor(divide(1000, 9)), 9), multiply(add(floor(divide(10, 9)), const_1), 9)), 9), const_1)