in the set of positive integers from 1 to 80 , what is the sum of all the odd multiples of 5 ?
"reduce to 1 - 80 5 - 15 - 25 - 35 - 45 - - 55 - - 65 - - 75 are valid multiples . add them - - > 320 c"
divide(multiply(80, multiply(const_3, 5)), 5)