how many numbers from 10 to 100 are exactly divisible by 9 ?
"option ' c ' 10 / 9 = 1 and 100 / 9 = 11 = = > 11 - 1 = 10 . therefore 10 digits ."
add(divide(subtract(multiply(floor(divide(100, 9)), 9), multiply(add(floor(divide(10, 9)), const_1), 9)), 9), const_1)