The ratio of gold content in 18K gold to other rare metals is 3:1. Now a piece of 18K gold jewelry weighing 20 grams, how many grams of gold is contained in it?
18K黄金中的金含量与其他稀有金属的比是3：1．现在一款重20克的18K黄金首饰，其中含金多少克？
<gadget id="calculator">1 + 3</gadget>
<output>4</output>

<gadget id="calculator">3 / 4</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">20 * (3/4)</gadget>
<output>15</output>

<result>15</result>