how many numbers from 15 to 65 are exactly divisible by 5 ?
"option ' d ' 15 / 5 = 3 and 65 / 5 = 13 = = > 13 - 3 = 10 numbers"
add(divide(subtract(multiply(floor(divide(65, 5)), 5), multiply(add(floor(divide(15, 5)), const_1), 5)), 5), const_1)