what is the sum of natural numbers between 20 and 100
"a = first number l = last number sn = n / 2 [ a + l ] between 20 and 100 numbers = 81 = > 100 - 20 = 80 + 1 = 81 sn = 81 / 2 × 120 = 81 × 60 = 4860 b )"
add(100, const_1)