There is a kind of duckweed growing in the pond. This kind of plant reproduces on the water surface and doubles in size every day. If after 10 days, the pond is just full of duckweed, how many days later, the duckweed in the pond will be just right? Take up half of the water?
池塘里生长着一种浮萍，这种植物在水面上繁殖，而且每天都能增长一倍，如果10天后，池塘里刚好长满这种浮萍，那么多少天后，池塘里的浮萍会正好占据了一半的水面？
<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<result>9</result>