Problem: a man has some hens and cows . if the number of heads be 50 and the number of feet equals 160 , then the number of hens will be :
Rationale: "explanation : let the number of hens be x and the number of cows be y . then , x + y = 50 . . . . ( i ) and 2 x + 4 y = 160 x + 2 y = 80 . . . . ( ii ) solving ( i ) and ( ii ) we get : x = 20 , y = 30 the required answer = 20 . answer : d"
annotated_formula: divide(subtract(multiply(50, const_4), 160), const_2)