The existing concentration of 40% sugar water is 8 kg, to obtain the concentration of 20% sugar water, how many kilograms of water need to be added.
现有浓度40%的糖水8千克，要得到浓度为20%的糖水，需要再加入水多少千克．
<gadget id="calculator">40 / 100</gadget>
<output>2/5 = around 0.4</output>

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

<gadget id="calculator">(2/5) / (1/5)</gadget>
<output>2</output>

<gadget id="calculator">8 * 2</gadget>
<output>16</output>

<gadget id="calculator">16 - 8</gadget>
<output>8</output>

<result>8</result>