How many kilograms of water should be added to 120 kg of salt water with a salt content of 5% to reduce the salt content to 3%.
在120千克含盐率为5%的盐水中，需加多少千克水才能使盐水的含盐率下降为3%．
<gadget id="calculator">5 / 100</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">3 / 100</gadget>
<output>3/100 = around 0.03</output>

<gadget id="calculator">(1/20) / (3/100)</gadget>
<output>5/3 = around 1.666667</output>

<gadget id="calculator">120 * (5/3)</gadget>
<output>200</output>

<gadget id="calculator">200 - 120</gadget>
<output>80</output>

<result>80</result>