There are 40 kg of brine with a salt content of 16%. After evaporating how many kg of water, the concentration can be increased to 20%.
有含盐16%的盐水40千克，蒸发多少千克水后可将浓度提高到20%．
<gadget id="calculator">16 / 100</gadget>
<output>4/25 = around 0.16</output>

<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(4/25) / (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">40 * (4/5)</gadget>
<output>32</output>

<gadget id="calculator">40 - 32</gadget>
<output>8</output>

<result>8</result>