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题库 / OG2017Q-PS-135
Machines A and B always operate independently and at their respective constant rates. When working alone, Machine A can fill a production lot in 5 hours, and Machine B can fill the same lot in x hours. When the two machines operate simultaneously to fill the production lot, it takes them 2 hours to complete the job.
What is the value of x ?
3~$1 \over 3$~
3
2~$1 \over 2$~
2~$1 \over 3$~
1~$1 \over 2$~
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