An alloy made of brass and gold. There are 40 grams of gold and 125 grams of brass. If the ratio of gold and brass in the alloy is 2:5, how many grams of gold should be added? (Solution by two methods, one of which should be solved by proportion)
用黄铜和黄金制成一种合金．现有黄金40克，黄铜125克，要使制成的合金中黄金和黄铜的比是2：5，还应加入多少克的黄金？(用两种方法解，其中一种要用比例解)
<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">125 * (2/5)</gadget>
<output>50</output>

<gadget id="calculator">50 - 40</gadget>
<output>10</output>

<result>10</result>