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How long will it take for two pipes A and B to fill an empty cistern

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Bunuel
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How long will it take for two pipes A and B to fill an empty cistern [#permalink] New post   21 Jan 2020, 04:38
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C
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E

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5% (low)

Question Stats:

90% (01:06) correct 10% (01:03) wrong based on 115 sessions
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How long will it take for two pipes A and B to fill an empty cistern if they worked alternately for an hour each?

(1) Working alone, Pipe A can fill the cistern in 40 hours
(2) Pipe B is one third as efficient as Pipe A
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C
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Re: How long will it take for two pipes A and B to fill an empty cistern [#permalink] New post   21 Jan 2020, 06:17
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Bunuel wrote:
How long will it take for two pipes A and B to fill an empty cistern if they worked alternately for an hour each?

(1) Working alone, Pipe A can fill the cistern in 40 hours
(2) Pipe B is one third as efficient as Pipe A


Question: Time taken to fill the cistern if they work alternately = ?

Statement 1: Working alone, Pipe A can fill the cistern in 40 hours

We do NOT know the rate of Pipe B hence

NOT SUFFICIENT

Statement 2: Pipe B is one third as efficient as Pipe A

B = A/3 but we need to calculate the time and we do NOT have any specifics of time taken by A and B hence

NOT SUFFICIENT

Combining the two statements

A fills in 40 hours i.e .Time of Pipe B = 3*30 = 120 hours

No we can find how much time will they take to fill the tank as we have the exact rates of pipes hence

SUFFICIENT

Answer: Option C
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Re: How long will it take for two pipes A and B to fill an empty cistern [#permalink] New post   22 Jan 2020, 01:35
#1
Working alone, Pipe A can fill the cistern in 40 hours Ra ; 1/40
Rb not know insufficient
#2
Rb = 1/3 * Ra ;
insufficient as Ra not know
from 1 & 2
we have Ra & Rb with us
IMO C sufficient
in 1 hr Ra ; 1/40 filled left with 39/40 which shall be fillled by b ; 117 hrs



Bunuel wrote:
How long will it take for two pipes A and B to fill an empty cistern if they worked alternately for an hour each?

(1) Working alone, Pipe A can fill the cistern in 40 hours
(2) Pipe B is one third as efficient as Pipe A
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Re: How long will it take for two pipes A and B to fill an empty cistern [#permalink] New post   30 Oct 2021, 22:46
GMATinsight wrote:
Bunuel wrote:
How long will it take for two pipes A and B to fill an empty cistern if they worked alternately for an hour each?

(1) Working alone, Pipe A can fill the cistern in 40 hours
(2) Pipe B is one third as efficient as Pipe A


Question: Time taken to fill the cistern if they work alternately = ?

Statement 1: Working alone, Pipe A can fill the cistern in 40 hours

We do NOT know the rate of Pipe B hence

NOT SUFFICIENT

Statement 2: Pipe B is one third as efficient as Pipe A

B = A/3 but we need to calculate the time and we do NOT have any specifics of time taken by A and B hence

NOT SUFFICIENT

Combining the two statements

A fills in 40 hours i.e .Time of Pipe B = 3*30 = 120 hours

No we can find how much time will they take to fill the tank as we have the exact rates of pipes hence

SUFFICIENT

Answer: Option C




GMATBusters


I think the OA is E, as we do not know, who has started the first A or B ? and we will have both different answers.
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Re: How long will it take for two pipes A and B to fill an empty cistern [#permalink] New post   22 Apr 2024, 16:11
Hi Bunuel, why is the answer to this question (C)? Should it not be (E)? I agree with hero_with_1000_faces that we do not know which pipe started working first, even if we know the rates of each pipe. So how can we say that we have sufficiency with the statements combined?
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Re: How long will it take for two pipes A and B to fill an empty cistern [#permalink] New post   23 Apr 2024, 01:02
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kkannan2 wrote:
Hi Bunuel, why is the answer to this question (C)? Should it not be (E)? I agree with hero_with_1000_faces that we do not know which pipe started working first, even if we know the rates of each pipe. So how can we say that we have sufficiency with the statements combined?

The point is that regardless of the order, the pipes require the same 30 hours to complete the job.
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Re: How long will it take for two pipes A and B to fill an empty cistern [#permalink]
23 Apr 2024, 01:02
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