There are 20kg of sugar water with a concentration of 20%, how many kilograms of water need to be added to obtain sugar water with a concentration of 10%?
现有浓度为20%的糖水20千克，要得到浓度为10%的糖水，需加水多少千克？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/5) / (1/10)</gadget>
<output>2</output>

<gadget id="calculator">20 * 2</gadget>
<output>40</output>

<gadget id="calculator">40 - 20</gadget>
<output>20</output>

<result>20</result>