The duckweed in the pond doubles every day, and the whole pond just grows in 10 days. After a few days of growing, the area of duckweed just accounts for one-eighth of the pond area.
池塘里的浮萍每天增一倍，10天刚好长满整个池塘．长了多少天时，浮萍的面积刚好占池塘面积的八分之一．
<gadget id="calculator">10 - 1 - 1 - 1</gadget>
<output>7</output>

<result>7</result>