The original 50kg of brine containing 10% salt, now want to increase its concentration to 20%, how many kg of water needs to be evaporated?
原有含盐10%的盐水50kg，现在要把它的浓度提高到20%，需要蒸发多少kg的水？
<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

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

<gadget id="calculator">(1/10) / (1/5)</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">50 * (1/2)</gadget>
<output>25</output>

<gadget id="calculator">50 - 25</gadget>
<output>25</output>

<result>25</result>