Use 50 kg of brine with a concentration of 25% to prepare brine with a concentration of 20%, how many kg of water should be added.
用浓度为25%的盐水50千克，配制成浓度为20%的盐水，还应加入清水多少千克．
<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

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

<gadget id="calculator">(1/4) / (1/5)</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">50 * (5/4)</gadget>
<output>125/2 = around 62.5</output>

<gadget id="calculator">(125/2) - 50</gadget>
<output>25/2 = around 12.5</output>

<result>25/2 = around 12.5</result>