pasture is full of grass, and the grass grows evenly every day. The grass on this pasture can feed 10 cows for 20 days, and it can also feed 15 cows for 10 days. So, how many days will the grass on this pasture last for 25 cows?
一块牧场长满了牧草，每天草都在匀度生长．这块牧场上的草可供10头牛吃20天，也可供15头牛吃10天．那么，这块牧场上的草可供25头牛吃多少天？
<gadget id="calculator">10 * 20</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>