how many multiples of 5 are there between 10 and 100 , exclusive ?
"5 * 2 = 10 5 * 20 = 100 total multiples = ( 20 - 2 ) + 1 = 19 exclude 10 and 100 = 19 - 2 = 17 answer is b"
add(divide(subtract(100, 10), 5), const_1)