In 500 grams of water, how many grams of salt should be added to obtain 20% salt water.
在500克水中，要加盐多少克可以得到含盐20%的盐水．
<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">500 / (4/5)</gadget>
<output>625</output>

<gadget id="calculator">625 - 500</gadget>
<output>125</output>

<result>125</result>