The salinity of a kind of brine is 20%, how much water should be added to turn 10kg of such brine into brine with a salinity of 10%.
一种盐水的含盐率是20%，10㎏这样的盐水要变成含盐率是10%的盐水，应加入多少水．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/5) / (1/10)</gadget>
<output>2</output>

<gadget id="calculator">10 * 2</gadget>
<output>20</output>

<gadget id="calculator">20 - 10</gadget>
<output>10</output>

<result>10</result>