题目

Most Americans enjoy moving from place to place. For example, they often drive their cars 120 to 160 kilometers away just to have dinner with a friend or even fly to Europe just for watching a football match. In some states only one person in five lives in a place for more than five years. One may be born in one city, and go to school in another. He may finish his middle school in two or three cities, and then attend a college far across the country. When he has entered business, he may possibly move from job to job. Moving from one job to another, which is called “job-hopping”, is 小明书房台灯的白炽灯泡额定功率是60W，为了节能，他把灯泡换成额定功率为10W的节能灯泡（两者亮度相当）．如果台灯每月正常工作100h，跟原来相比，这盏灯每月可节约    kW?h的电能．