meadow is covered with grass, and the grass grows at the same rate every day. Now this pasture can feed 10 cows for 20 days, or feed 15 cows for 10 days. How many days can it feed 25 cows?
一片草场长满青草，而且青草每天生长的速度相等．现在这片草场可供10头牛吃20天，或者供15头牛吃10天，若供25头牛能吃多少天．
<gadget id="calculator">20 * 10</gadget>
<output>200</output>

<gadget id="calculator">15 * 10</gadget>
<output>150</output>

<gadget id="calculator">200 - 150</gadget>
<output>50</output>

<gadget id="calculator">20 - 10</gadget>
<output>10</output>

<gadget id="calculator">50 / 10</gadget>
<output>5</output>

<gadget id="calculator">5 * 20</gadget>
<output>100</output>

<gadget id="calculator">200 - 100</gadget>
<output>100</output>

<gadget id="calculator">25 - 5</gadget>
<output>20</output>

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

<result>5</result>