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【OG20-P164-118题】
Three printing presses, R, S, and T, working together at their respective constant rates, can do a certain printing job in 4 hours. S and T, working together at their respective constant rates, can do the same job in 5 hours. How many hours would it take R, working alone at its constant rate, to do the same job?
分析A选项
分析B选项
分析C选项
分析D选项
分析E选项
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【答案】E
【解析】
R,S,T一起完成任务需要4小时，所以三人的速度和是1/4。
S,T一起完成任务需要5小时，所以两人的速度和是1/5。
设R的速度是x/小时，那么x+1/5=1/4，解得x=1/20，所以R完成相同的任务所需时间是20小时。
【知识补充】
工作效率=工作总量÷时间
999+
请问这种题可以直接4x5来算吗？
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2021-10-12 12:29:07
EricaKo
设总printing job完成量为a，R+S+T的每小时的效率是a/4，S+T的每小时效率是a/5，相减得出R的每小时效率是a/20，所以R需要a/(a/20)=20小时独立完成。
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2018-08-03 15:36:59
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