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Director  B
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How many hours would it take Pump A and Pump B working together, each  [#permalink]

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49 00:00

Difficulty:   45% (medium)

Question Stats: 59% (01:17) correct 41% (00:55) wrong based on 967 sessions

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How many hours would it take Pump A and Pump B working together, each at its own constant rate, to empty a tank that was initially full?

(1) Working alone at its constant rate,Pump A would empty the full tank in 4 hours 20 minutes.
(2) Working alone, Pump B would empty the full tank at its constant rate of 72 liters per minute.

OG Q 2017 New Question(Book Question: 186)

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GMAT 1: 750 Q49 V43 Re: How many hours would it take Pump A and Pump B working together, each  [#permalink]

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AbdurRakib wrote:
How many hours would it take Pump A and Pump B working together,each at its own constant rate,to empty a tank that was initially full?

(1) Working alone at its constant rate,Pump A would empty the full tank in 4 hours 20 minutes.
(2) Working alone,Pump B would empty the full tank at its constant rate of 72 liters per minute.

OG Q 2017 New Question(Book Question: 186)

(1) Working alone at its constant rate,Pump A would empty the full tank in 4 hours 20 minutes.
A will empty the tank in 260 minutes.
Rate of A * 260min= VOLUME TO BE EMPTIED
We don't know the rate of A or volume of the tank
INSUFFICIENT

(2) Working alone,Pump B would empty the full tank at its constant rate of 72 liters per minute.
B's rate is 72 litre per minute.
72*time = volume
We don't know volume of the tank so or how much time B takes to empty.
INSUFFICIENT

Combining 1 and 2, we still don't know the total water in the tank
rate of A*260 = 72*time of B
Even if we change rate into time or time into rate, we will still have two unknowns {volume and time} or {volume or rate}
{V and R } or {V and T}

Obvious enough we still cannot solve this equation because we do not know the volume

INSUFFICIENT

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Re: How many hours would it take Pump A and Pump B working together, each  [#permalink]

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1
E

A)A's rate is there
B)B's rate is given in litre/min

1+2
not suff
We don't know the total time for B to empty tank
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Re: How many hours would it take Pump A and Pump B working together, each  [#permalink]

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1. A can empty the tank in 4 hours and 20 minutes but no information on B so insufficient.
2. B's rate is given in litres/min instead of time taken .
Therefore E
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How many hours would it take Pump A and Pump B working together, each  [#permalink]

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Hello guys...

I know that this is a simple problem but I have questions.

In many work/rate problems we create the WRT table and after having the 4hrs and 20 min for (1) we assume that the total work equals 1 and we have the rate which is 1/(time of pump A to complete the work). This basically helps us determine the % of completion per hour!

In (2) we are given the actual rate which is understandable that doesn't help since we don't know the total liters or total time.

Q1: Is it wrong to say that the rate for pump A from (1) is 1/(4hrs 20mins) meaning 23% of the work per hour?
Q2: Logically since we know from (1) the rate and from (2) the rate we can find the total time by adding the two rates and find the reciprocal of the result. Why we can't do that?
Q3: If we had on (2) the time of completion the (1+2) would be SUFFICIENT? -- We could use the same logic as (1).

Please let me know. I must have missed something...

Bunuel VeritasPrepKarishma

Originally posted by standyonda on 27 May 2018, 00:10.
Last edited by standyonda on 03 Jul 2018, 00:53, edited 1 time in total.
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Re: How many hours would it take Pump A and Pump B working together, each  [#permalink]

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gmatbusters niks18 VeritasPrepKarishma amanvermagmat pushpitkc

Quote:
How many hours would it take Pump A and Pump B working together, each at its own constant rate, to empty a tank that was initially full?

(1) Working alone at its constant rate,Pump A would empty the full tank in 4 hours 20 minutes.
(2) Working alone, Pump B would empty the full tank at its constant rate of 72 liters per minute.

Even if the total volume of tank is given hypothetically, can we safely assume that the rate of emptying the tank is
same for A and B ?
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Re: How many hours would it take Pump A and Pump B working together, each  [#permalink]

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can we safely assume that the rate of emptying the tank is same for A and B ? - NO

Don't ever assume so unless explicitly mentioned.

gmatbusters niks18 VeritasPrepKarishma amanvermagmat pushpitkc

Quote:
How many hours would it take Pump A and Pump B working together, each at its own constant rate, to empty a tank that was initially full?

(1) Working alone at its constant rate,Pump A would empty the full tank in 4 hours 20 minutes.
(2) Working alone, Pump B would empty the full tank at its constant rate of 72 liters per minute.

Even if the total volume of tank is given hypothetically, can we safely assume that the rate of emptying the tank is
same for A and B ?

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Intern  B
Joined: 31 Aug 2016
Posts: 45
How many hours would it take Pump A and Pump B working together, each  [#permalink]

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standyonda wrote:
Hello guys...

I know that this is a simple problem but I have questions.

In many work/rate problems we create the WRT table and after having the 4hrs and 20 min for (1) we assume that the total work equals 1 and we have the rate which is 1/(time of pump A to complete the work). This basically helps us determine the % of completion per hour!

In (2) we are given the actual rate which is understandable that doesn't help since we don't know the total liters or total time.

Q1: Is it wrong to say that the rate for pump A from (1) is 1/(4hrs 20mins) meaning 23% of the work per hour?
Q2: Logically since we know from (1) the rate and from (2) the rate we can find the total time by adding the two rates and find the reciprocal of the result. Why we can't do that?
Q3: If we had on (2) the time of completion the (1+2) would be SUFFICIENT? -- We could use the same logic as (1).

Please let me know. I must have missed something...

Bunuel VeritasPrepKarishma

VeritasPrepKarishma can you check the Qs please?

Originally posted by standyonda on 12 Jun 2018, 07:59.
Last edited by standyonda on 03 Jul 2018, 00:53, edited 1 time in total.
Intern  S
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Posts: 48
Re: How many hours would it take Pump A and Pump B working together, each  [#permalink]

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hi standyonda,

Not at all expert but I thought same as you and marked C but later realised that problem never tells us that both pumps are attached to same tank.
We assumed that both pumps are of same tank and solved taking capacity as 1.
Should not have assumed this.

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How many hours would it take Pump A and Pump B working together, each  [#permalink]

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manasveek wrote:
hi standyonda,

Not at all expert but I thought same as you and marked C but later realised that problem never tells us that both pumps are attached to same tank.
We assumed that both pumps are of same tank and solved taking capacity as 1.
Should not have assumed this.

The issue here is that on (1) we can say that {1 work} is {1 full tank emptied per min} so this is our measurement unit for {work}. However with (2) we have {litres per minute} so it obviously doesn't make any sense to solve it using both statements and work=1.
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GMAT 1: 420 Q26 V13 GMAT 2: 540 Q44 V21 Re: How many hours would it take Pump A and Pump B working together, each  [#permalink]

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1
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Re: How many hours would it take Pump A and Pump B working together, each  [#permalink]

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AbdurRakib wrote:
How many hours would it take Pump A and Pump B working together, each at its own constant rate, to empty a tank that was initially full?

(1) Working alone at its constant rate,Pump A would empty the full tank in 4 hours 20 minutes.
(2) Working alone, Pump B would empty the full tank at its constant rate of 72 liters per minute.

OG Q 2017 New Question(Book Question: 186)

could some one please provide a scenario in which the total is known? I'm having a difficult time seeing how knowing the total number of gallons (or what other measurement you want to use) in the tank matters since we have the rate at which both pumps could complete the job.
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Re: How many hours would it take Pump A and Pump B working together, each  [#permalink]

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aaronhew wrote:
AbdurRakib wrote:
How many hours would it take Pump A and Pump B working together, each at its own constant rate, to empty a tank that was initially full?

(1) Working alone at its constant rate,Pump A would empty the full tank in 4 hours 20 minutes.
(2) Working alone, Pump B would empty the full tank at its constant rate of 72 liters per minute.

OG Q 2017 New Question(Book Question: 186)

could some one please provide a scenario in which the total is known? I'm having a difficult time seeing how knowing the total number of gallons (or what other measurement you want to use) in the tank matters since we have the rate at which both pumps could complete the job.

Okay, now let me make one thing clear.... Statement 1 provides the *time* taken by pump A to empty the tank.. on the other hand, statement 2 provides the *rate* at which pump B works...

We either need to have the actual capacity of the tank or the rate at which pump A works...

Posted from my mobile device Re: How many hours would it take Pump A and Pump B working together, each   [#permalink] 21 Mar 2019, 19:02
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