How many kilograms of water need to be evaporated to turn 50 kg of brine containing 10% salinity into brine containing 20% salinity?
将含盐10%的盐水50千克变成含盐率为20%的盐水，需蒸发多少千克水．
<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>