In a group of cows and chickens, the number of legs was 20 more than twice the number of heads. The number of cows was: Options:
A) 5
B) 7
C) 10
D) 12
E) 14

Rationale: "let the number of cows be x and their legs be 4 x . let the number of chicken be y and their legs be 2 x . total number of legs = 4 x + 2 y . total number of heads = x + y . the number of legs was 20 more than twice the number of heads . therefore , 2 × ( x + y ) + 20 = 4 x + 2 y . or , 2 x + 2 y + 20 = 4 x + 2 y . or , 2 x + 20 = 4 x [ subtracting 2 y from both sides ] . or , 20 = 4 x – 2 x [ subtracting 2 x from both sides ] . or , 20 = 2 x . or , x = 10 [ dividing by 2 on both sides ] . therefore , the number of cows = 10 . correct answer : c ) 10"
Answer: C