The concentration of a liquid medicine is 20%. Now there are 15 kilograms of liquid medicine, how many kilograms of water need to be added.
一种药水的浓度是20%，现在有药液15千克，需要加水多少千克．
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">15 / (1/5)</gadget>
<output>75</output>

<gadget id="calculator">75 - 15</gadget>
<output>60</output>

<result>60</result>