The area of duckweed in a pond doubles every day, the entire pond is covered in 8 days, and half of the pond is covered in the first few days.
一个水塘里的浮萍面积每天增加1倍，8天长满整个水塘，第多少天长满水塘的一半．
<gadget id="calculator">8 - 1</gadget>
<output>7</output>

<result>7</result>