Uncle Li was going to work at the company at 3:00 pm. He estimated that it was almost time to go to work, so he went inside to watch the clock, but the clock stopped at 12:20 because the battery was exhausted. He replaced the clock with fresh batteries, but forgot to set the hands to the correct time. He left home in a hurry and went to the company to see that there were still 10 minutes before the work time, and he left work at 10:50 in the evening. Uncle Li returned home and saw the clock until 8:50. , Then how long did the clock stop in his house?
李叔叔下午3点要到公司上班，他估计快到上班时间了，到屋里看钟，可是钟因电池能量耗尽早在12：20停了．他给钟换上了新电池，但却忘了把指针拨到正确的时间．他匆匆离家，到公司一看，离上班时间还有10分钟，晚上10：50下班，李叔叔回到家里，一看钟才8：50，假定李叔叔上班和下班在路上用的时间相同，那么他家的钟停了多少时．
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