An alloy of copper and zinc contains copper and zinc in the ratio 5 : 4. Another alloy of copper and zinc contains copper and zinc in the ratio 3 : 6. In what ratio should the two alloys be mixed so that the resultant alloy contains equal proportions of copper and zinc?	Choices:
A) 4 : 1  B) 6 : 1  C) 1 : 3  D) 2 : 1  E) 4 : 1

Rationale: let alloy _ 1 be x units , and let alloy _ 2 be y units . so , fraction of copper in alloy _ 1 = 5 x / 9 , and fraction of zinc in alloy _ 1 = 4 x / 9 . similarly , fraction of copper in alloy _ 2 = 3 y / 9 , and fraction of zinc in alloy _ 2 = 6 y / 9 . mixing them , we get copper = 5 x / 9 + 3 y / 9 ; zinc = 4 x / 9 + 6 y / 9 so , 5 x + 3 y = 4 x + 6 y - > x = 3 y - > x / y = 1 / 3 so , they must be mixed in the ratio 1 : 3 answer : c
Answer: C