A sugar water with a sugar content of 25% is 400g, how many grams of water need to be added in order to obtain a sugar water with a sugar content of 20%?
一种含糖率25%的糖水400g，为了得到含糖率20%的糖水，需要加水多少克？
<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

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

<gadget id="calculator">(1/4) / (1/5)</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">400 * (5/4)</gadget>
<output>500</output>

<gadget id="calculator">500 - 400</gadget>
<output>100</output>

<result>100</result>