There are 500 grams of salt water with a salt content of 12%. How many grams of water are evaporated to obtain salt water with a salt content of 15%.
有含盐12%的盐水500克，蒸发掉多少克水，就可以得到含盐15%的盐水．
<gadget id="calculator">12 / 100</gadget>
<output>3/25 = around 0.12</output>

<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">(3/25) / (3/20)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">500 * (4/5)</gadget>
<output>400</output>

<gadget id="calculator">500 - 400</gadget>
<output>100</output>

<result>100</result>