There is a piece of grass in the pasture, which grows at the same rate every year. This piece of grass can feed 10 cows for 20 days, or 15 cows for 10 days. If it is now necessary to feed 25 cows, how many days can it eat?
牧场上有一片青草，每年都生长的一样快，这片青草可供10头牛吃20天，或供15头牛吃10天，如果现在要供给25头牛吃，可吃多少天．
<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>