There are 50 kilograms of brine with a salt content of 20%, how many kilograms of water should be evaporated to make the brine contain 25% salt?
有含盐20%的盐水50千克，要使盐水含盐率为25%，应蒸发掉多少千克水？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">(1/5) / (1/4)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">50 * (4/5)</gadget>
<output>40</output>

<gadget id="calculator">50 - 40</gadget>
<output>10</output>

<result>10</result>