how many multiples of 3 are there between 10 and 100 , exclusive ?
"3 * 4 = 12 3 * 33 = 99 total multiples = ( 33 - 4 ) + 1 = 30 exclude 10 and 100 = 30 answer is a"
add(divide(subtract(100, 10), 3), const_1)