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Math Expert
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Re: Machine A, working alone at its constant rate, manufactures 280 bolts [#permalink]
Bunuel wrote:
Machine A, working alone at its constant rate, manufactures 280 bolts per hour, and machine B, working alone at its constant rate, manufactures 220 bolts per hour. How many hours will it take for machines A and B, working together at their respective constant rates,to manufacture 1,000 bolts?

A. 1
B. 1.3
C. 1.5
D. 1.8
E. 2

Since the efficiency of both the machines are given it boils down to -

\(\frac{1000}{(220 + 280)} = 2\) Hours, Answer must be (E)
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Re: Machine A, working alone at its constant rate, manufactures 280 bolts [#permalink]
Expert Reply
Bunuel wrote:
Machine A, working alone at its constant rate, manufactures 280 bolts per hour, and machine B, working alone at its constant rate, manufactures 220 bolts per hour. How many hours will it take for machines A and B, working together at their respective constant rates,to manufacture 1,000 bolts?

A. 1
B. 1.3
C. 1.5
D. 1.8
E. 2


Since the combined rate is 500 bolts per hour, then it will take 1,000/500 = 2 hours for the two machines to manufacture 1,000 bolts.

Answer: E
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Re: Machine A, working alone at its constant rate, manufactures 280 bolts [#permalink]
In one hour total bolts made=280+220=>500 bolts
500 bolts in 1 hr
So, 1000 bolts in 2 hrs.
(E)
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Re: Machine A, working alone at its constant rate, manufactures 280 bolts [#permalink]
Hello from the GMAT Club BumpBot!

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Re: Machine A, working alone at its constant rate, manufactures 280 bolts [#permalink]
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