The weight ratio of copper to tin in a copper-tin alloy is 5:7. Now there are 3500 kg of copper, how much tin needs to be added to make this alloy? (Solve with ratio)
一种铜锡合金中铜与锡的重量比是5：7．现在有3500千克铜，需要加多少锡才能制成这种合金？(用比例解)
<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">3_500 / (5/7)</gadget>
<output>4_900</output>

<result>4_900</result>