In 100 grams of salt water containing 5% salt, how many grams of water should be added to obtain salt water containing 1% salt?
在含盐5%的100克盐水中，要得到含盐1%的盐水，要加水多少克．
<gadget id="calculator">5 / 100</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">100 * (1/20)</gadget>
<output>5</output>

<gadget id="calculator">1 / 100</gadget>
<output>1/100 = around 0.01</output>

<gadget id="calculator">5 / (1/100)</gadget>
<output>500</output>

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

<result>400</result>