There is 500 ml of salt water with 3% salt content, how many milliliters of water is added to become salt water with 2% salt content.
有含盐3%的盐水500毫升，加入多少毫升的水就变成含盐2%的盐水．
<gadget id="calculator">3 / 100</gadget>
<output>3/100 = around 0.03</output>

<gadget id="calculator">2 / 100</gadget>
<output>1/50 = around 0.02</output>

<gadget id="calculator">(3/100) / (1/50)</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">500 * (3/2)</gadget>
<output>750</output>

<gadget id="calculator">750 - 500</gadget>
<output>250</output>

<result>250</result>