Xiao Qiao puts glass balls in a rectangular box, and the number of glass balls she puts in the box doubles every minute. If this goes on for 10 minutes, it will be filled exactly, so how many minutes, the box will be filled exactly half.
小巧往一个长方形盒子里放玻璃球，她往盒子里放的玻璃球个数每分钟增加1倍，这样下去10分钟正好放满，那么多少分钟时，恰好放满半个盒子．
<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<result>9</result>