There is a watch that is 30 seconds behind the alarm clock every hour, and the alarm clock is 30 seconds ahead of the standard time. If you align the watch and the alarm clock at 12 noon, at 8 o'clock that night, the watch is a few seconds behind the standard time.
有一块手表比闹钟每小时慢30秒，闹钟比标准时间每小时快30秒，中午12点把手表和闹钟都对准，当天晚上8点，手表比标准时间慢几秒．
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