How many grams of water needs to be evaporated to turn 500 grams of salt water containing 2% salt into salt water containing 5% salt?
将含盐2%的盐水500克，变成含盐5%的盐水，需要蒸发出水多少克．
<gadget id="calculator">2 / 100</gadget>
<output>1/50 = around 0.02</output>

<gadget id="calculator">5 / 100</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/50) / (1/20)</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">500 * (2/5)</gadget>
<output>200</output>

<gadget id="calculator">500 - 200</gadget>
<output>300</output>

<result>300</result>