An alloy is composed of metals A and B according to a certain mass ratio. The market price ratio of A and B is 2:3, and the price of the alloy is determined accordingly. This year, the price of metal A will decrease by 20%, and the price of metal B will increase by 20%. But the cost of this alloy remains unchanged. From this we can know, what percentage of the mass of metal A in this alloy?
某合金由金属A和B按一定的质量比组成，A和B的市场价格比为2：3，并由此确定合金价格，今年金属A的价格下降20%，金属B的价格上升20%，但这种合金的成本不变，由此可知，这种合金中金属A的质量占百分之几？
<gadget id="calculator">3.6 - 3</gadget>
<output>0.6</output>

<result>0.6</result>