Shanghai World Expo special buses No. 1, No. 2 and No. 3 depart from the starting point at 6:00 a.m. at the same time. Route 1 departs every 10 minutes, Route 2 departs every 12 minutes, Route 3 departs every 15 minutes, when should they depart at the same time next time?
上海世博会专用公交车1路、2路和3路早上6时同时从起点出发．1路每隔10分钟发一班车，2路每隔12分钟发一班车，3路每隔15分钟发一班车，它们下次同时发车应是什么时间？
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