Problem: find the average of all prime numbers between 30 and 50 ?
Rationale: "there are five prime numbers between 30 and 50 . they are 31,37 , 41,43 and 47 . therefore the required average = ( 31 + 37 + 41 + 43 + 47 ) / 5  199 / 5  39.8 answer c 39.8"
annotated_formula: divide(add(add(add(30, const_1), add(add(30, const_1), const_2)), add(subtract(50, 30), subtract(50, const_2))), 30)