Take 50 grams of salt water containing 8% salt, how many grams of water must be evaporated to make the salt water contain 20% salt
把含盐8%的盐水50克，蒸发掉多少克水后，才能使盐水含盐20%
<gadget id="calculator">8 / 100</gadget>
<output>2/25 = around 0.08</output>

<gadget id="calculator">50 * (2/25)</gadget>
<output>4</output>

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

<gadget id="calculator">4 / (1/5)</gadget>
<output>20</output>

<gadget id="calculator">50 - 20</gadget>
<output>30</output>

<result>30</result>