In 500 grams of salt water with a salt content of 8%, if the weight of the water contained remains the same, how many grams of salt should be added to obtain a salt water with a salt content of 20%.
在含盐8%的500克盐水中，如果所含水的重量不变，要想得到含盐率为20%的盐水，要加盐多少克．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">500 * (1/5)</gadget>
<output>100</output>

<gadget id="calculator">8 / 100</gadget>
<output>2/25 = around 0.08</output>

<gadget id="calculator">500 * (2/25)</gadget>
<output>40</output>

<gadget id="calculator">100 - 40</gadget>
<output>60</output>

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

<gadget id="calculator">60 / (4/5)</gadget>
<output>75</output>

<result>75</result>