If there are 500 grams of salt water with 20% salt content, how many grams of water should be added to make salt water with 10% salt content?
现有含盐20%的盐水500克，要配制成含盐10%的盐水，需加水多少克．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/5) / (1/10)</gadget>
<output>2</output>

<gadget id="calculator">500 * 2</gadget>
<output>1_000</output>

<gadget id="calculator">1_000 - 500</gadget>
<output>500</output>

<result>500</result>