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GRE Math Challenge #26-Pump A can empty a pool in 8 minutes
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Updated on: 21 May 2024, 22:27
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57% (02:01) correct
42% (02:01) wrong based on 35 sessions
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Pump A can empty a pool in 8 minutes.Pump B can empty a pool in 6 minutes.Pump A pumps the pool for 2 minutes before pump B joins in.How may minutes will it take to empty the pool together?
Re: GRE Math Challenge #26-Pump A can empty a pool in 8 minutes
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24 Aug 2016, 05:56
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sandy wrote:
Pump A can empty a pool in 8 minutes.Pump B can empty a pool in 6 minutes.Pump A pumps the pool for 2 minutes before pump B joins in.How may minutes will it take to empty the pool together?
Let's assign a nice value for the volume of the pool and go from there.
Pump A can empty a pool in 8 minutes.Pump B can empty a pool in 6 minutes. The least common multiple of 8 and 6 is 24. So, let's say that the TOTAL volume of the pool is 24 gallons.
If pump A can empty a pool in 8 minutes, then pump A's rate = 24 gallons/8 minutes = 3 gallons per minute If pump B can empty a pool in 6 minutes, then pump B's rate = 24 gallons/6 minutes = 4 gallons per minute So, there COMBINED rate = 3 + 4 = 7 gallons per minute
Pump A pumps the pool for 2 minutes before pump B joins in.How may minutes will it take to empty the pool together? First 2 minutes: At a rate of 3 gallons per minute, pump A removes 6 gallons from the pool, which means the amount REMAINING in the pool = 24 - 6 = 18 gallons
At a COMBINED rate of 7 gallons per minute, the time it takes to remove the remaining 18 gallons = 18/7 minutes
So, the TOTAL TIME it takes to empty the pool = 2 minutes (pump A alone) + 18/7 minutes (together) = 32/7 minutes
Re: GRE Math Challenge #26-Pump A can empty a pool in 8 minutes
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28 Jul 2017, 03:12
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Hi Brent, I did the same calculations that you did, but at the end of the problem I subtracted 2 minutes from 4.57 minutes because during those two minutes the machines were not working together. I was confused by the wording of the question since it asked for the time it took for the machines to empty the pool together, so I thought the answer would be 2.57 minutes. Will the questions on the GRE be phrased like this as well? Amy
Re: GRE Math Challenge #26-Pump A can empty a pool in 8 minutes
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28 Jul 2017, 05:16
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AmyK wrote:
Hi Brent, I did the same calculations that you did, but at the end of the problem I subtracted 2 minutes from 4.57 minutes because during those two minutes the machines were not working together. I was confused by the wording of the question since it asked for the time it took for the machines to empty the pool together, so I thought the answer would be 2.57 minutes. Will the questions on the GRE be phrased like this as well? Amy
I have a feeling, the test-makers would add some extra information to prevent ambiguity. Perhaps something like...
Pump A can empty a pool in 8 minutes. Pump B can empty a pool in 6 minutes. At 1:00pm Pump A starts pumping the pool. At 1:02pm, pump B joins in. At what time with the pool be empty?
Re: GRE Math Challenge #26-Pump A can empty a pool in 8 minutes
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25 Dec 2017, 05:30
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sandy wrote:
Pump A can empty a pool in 8 minutes.Pump B can empty a pool in 6 minutes.Pump A pumps the pool for 2 minutes before pump B joins in.How may minutes will it take to empty the pool together?
can you check the answer, since the stem says empty the pool together, I thought the answer is 18/7?