How much water must be distilled from 40 grams of salt water with a salt content of 16% to produce salt water with a salt content of 20%.
要从40克含盐率为16%的盐水中蒸去多少水，才能制成含盐率为20%的盐水．
<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>