An alloy of copper and zinc contains copper and zinc in the ratio 9 : 6. Another alloy of copper and zinc contains copper and zinc in the ratio 6 : 9. In what ratio should the two alloys be mixed so that the resultant alloy contains equal proportions of copper and zinc?  Choose the correct choice from the following:
A) 1 : 5
B) 1 : 4
C) 1 : 3
D) 1 : 1
E) 1 : 2
Let Alloy_1 be x units, and let Alloy_2 be y units.   So, fraction of copper in Alloy_1 = 9x/15, and fraction of zinc in Alloy_1 = 6x/15   Similarly, fraction of copper in Alloy_2 = 6y/15, and fraction of zinc in Alloy_2 = 9y/15.   Mixing them, we get   copper = 9x/15 +6y/15; zinc = 6x/15 + 9y/15   So, 9x+6y = 6x+9y   -&gt; 3x = 3y   -&gt; x/y =3/3= 
<gadget id="calculator">3/3</gadget>
<output>1</output>
1/1   So, they must be mixed in the ratio 1 : 1   Answer : 1 : 1
<result>D</result>
An alloy of copper and zinc contains copper and zinc in the ratio 9 : 6. Another alloy of copper and zinc contains copper and zinc in the ratio 6 : 9. In what ratio should the two alloys be mixed so that the resultant alloy contains equal proportions of copper and zinc?