The area of the water lilies in the pond doubles every day. If it takes 12 days to cover the entire pond, how many days will it take for these water lilies to cover half of the pond?
池塘里的睡莲的面积每天长大一倍，若经过12天就可以长满整个池塘，则这些睡莲长满半个池塘需要多少天．
<gadget id="calculator">12 - 1</gadget>
<output>11</output>

<result>11</result>