In 100 grams of salt water containing 10% salt, how many grams of water are needed to make the salt water 5% salt.
在含盐10%的100克盐水中，需要多少克水，才能使盐水含盐5%．
<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

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

<gadget id="calculator">(1/10) / (1/20)</gadget>
<output>2</output>

<gadget id="calculator">100 * 2</gadget>
<output>200</output>

<gadget id="calculator">200 - 100</gadget>
<output>100</output>

<result>100</result>