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题库 / Prep2007E1-PS-146
Machine A, working alone atits constant rate, manufactures 280 bolts per hour, and machine B, working aloneat its constant rate, manufactures 220 bolts per hour. How many hours will it take for machines Aand B, working together at their respective constant rates, to manufacture1,000 bolts?
1
1.3
1.5
1.8
2
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