40 kilograms of brine with a salt content of 10% is converted into brine with a saline content of 5%.
含盐10%的盐水40千克，要把它变成含盐率为5%的盐水要怎么办？
<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">5 / 100</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/10) / (1/20)</gadget>
<output>2</output>

<gadget id="calculator">40 * 2</gadget>
<output>80</output>

<gadget id="calculator">80 - 40</gadget>
<output>40</output>

<result>40</result>