In a group of cows and hens, the number of legs are 18 more than twice the number of heads. The number of cows is  Choose the correct choice from the following.
A) 5  B) 7  C) 9  D) 12  E) 14
Explanation:   Let the number of cows be x and the number of hens be y.   Then, 4x + 2y = 2 (x + y) + 18   4x + 2y = 2x + 2y + 18   2x = 18   x = 9.   Answer: 9
<result>C</result>
In a group of cows and hens, the number of legs are 18 more than twice the number of heads. The number of cows is