How many grams of water need to be evaporated to turn 400 grams of 16% salt water into 20% salt water?
把16%的盐水400克，变成20%的盐水需蒸发掉多少克水．
<gadget id="calculator">16 / 100</gadget>
<output>4/25 = around 0.16</output>

<gadget id="calculator">400 * (4/25)</gadget>
<output>64</output>

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

<gadget id="calculator">64 / (1/5)</gadget>
<output>320</output>

<gadget id="calculator">400 - 320</gadget>
<output>80</output>

<result>80</result>