There is 200 kilograms of a pesticide with a concentration of 25%, how many kilograms of water need to be added to obtain a pesticide with a concentration of 10%?
有一种浓度为25%的农药200千克，为了得到浓度为10%的农药，需加水多少千克？
<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

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

<gadget id="calculator">(1/4) / (1/10)</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">200 * (5/2)</gadget>
<output>500</output>

<gadget id="calculator">500 - 200</gadget>
<output>300</output>

<result>300</result>