How many kilograms of salt should be added to turn 30 kg of salt water with 20% salt into salt water with 25% salt?
含盐20%的盐水30千克变成含盐25%的盐水，要加盐多少千克．
<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">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 - (1/4)</gadget>
<output>3/4 = around 0.75</output>

<gadget id="calculator">(4/5) / (3/4)</gadget>
<output>16/15 = around 1.066667</output>

<gadget id="calculator">30 * (16/15)</gadget>
<output>32</output>

<gadget id="calculator">32 - 30</gadget>
<output>2</output>

<result>2</result>