How many grams of water should be added to dilute 400 grams of salt water with a salt content of 5% to 4% salt water?
把含盐率为5%的400克盐水稀释成含盐率是4%的盐水，应加水多少克？
<gadget id="calculator">5 / 100</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">4 / 100</gadget>
<output>1/25 = around 0.04</output>

<gadget id="calculator">(1/20) / (1/25)</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>