There are 30 kilograms of pesticides with a concentration of 60%, and now you want to dilute it into a potion with a concentration of 15%, how many kilograms of water need to be added.
有30千克浓度为60%的农药，现在要把它稀释成浓度为15%的药水，需要加水多少千克．
<gadget id="calculator">60 / 100</gadget>
<output>3/5 = around 0.6</output>

<gadget id="calculator">30 * (3/5)</gadget>
<output>18</output>

<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">30 * (3/20)</gadget>
<output>9/2 = around 4.5</output>

<gadget id="calculator">18 - (9/2)</gadget>
<output>27/2 = around 13.5</output>

<gadget id="calculator">(27/2) / (3/20)</gadget>
<output>90</output>

<result>90</result>