There is 40kg of salt water with 8% salt content, how much salt should be added to the salt water to make the salt water 20% salt.
现有含盐8%的盐水40kg，要将盐水配成含盐20%，需要向盐水中加盐多少kg．
<gadget id="calculator">8 / 100</gadget>
<output>2/25 = around 0.08</output>

<gadget id="calculator">1 - (2/25)</gadget>
<output>23/25 = around 0.92</output>

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

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

<gadget id="calculator">(23/25) / (4/5)</gadget>
<output>23/20 = around 1.15</output>

<gadget id="calculator">40 * (23/20)</gadget>
<output>46</output>

<gadget id="calculator">46 - 40</gadget>
<output>6</output>

<result>6</result>