It is currently 20 Oct 2017, 16:44

### GMAT Club Daily Prep

#### Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# Working together at their constant rates, A and B can fill

Author Message
TAGS:

### Hide Tags

Manager
Joined: 03 Feb 2010
Posts: 68

Kudos [?]: 149 [2], given: 4

Working together at their constant rates, A and B can fill [#permalink]

### Show Tags

15 Jul 2010, 15:50
2
KUDOS
13
This post was
BOOKMARKED
00:00

Difficulty:

35% (medium)

Question Stats:

61% (00:52) correct 39% (00:47) wrong based on 644 sessions

### HideShow timer Statistics

Working together at their constant rates, A and B can fill an empty tank to capacity in 1/2 hours. What is the constant rate of pump B?

(1) A's constant rate is 25 LTS / min
(2) The tanks capacity is 1200 lts.
[Reveal] Spoiler: OA

Last edited by Bunuel on 09 Nov 2012, 05:16, edited 1 time in total.
Edited the question.

Kudos [?]: 149 [2], given: 4

Math Expert
Joined: 02 Sep 2009
Posts: 41892

Kudos [?]: 129034 [2], given: 12187

Re: Data sufficiency work rate problem [#permalink]

### Show Tags

16 Jul 2010, 08:10
2
KUDOS
Expert's post
5
This post was
BOOKMARKED
ksharma12 wrote:
15. working together at their constant rates , A and B can fill an empty tank to capacity in1/2 hr.what is the constant rate of pump B?
1) A's constant rate is 25LTS / min
2) the tanks capacity is 1200 lts.

Can someone solve this beyond just showing what is sufficient?

I know the answer is A but I need to know how to solve to fully grasp the concept of only needing the first statement.

Thank you

Answer to this question is C not A.

$$rate*time=job$$.

We are told that $$(A+B)*30=C$$, where $$A$$ is the rate of pump A in lts/min, $$B$$ is the rate of pump B in lts/min and C is the capacity of the tank in liters.

Question: $$B=?$$

(1) $$A=25$$ --> $$(25+B)*30=C$$ --> clearly insufficient (two unknowns), if $$C=1200$$, then $$B=15$$ but of $$C=1500$$, then $$B=25$$.

(2) $$C=1200$$. $$(A+B)*30=1200$$ --> $$A+B=40$$. Also insufficient.

(1)+(2) $$A=25$$ and $$A+B=40$$ --> $$B=15$$. Sufficient.

_________________

Kudos [?]: 129034 [2], given: 12187

Director
Joined: 25 Apr 2012
Posts: 724

Kudos [?]: 847 [2], given: 724

Location: India
GPA: 3.21
Re: working together at their constant rates , A and B can fill [#permalink]

### Show Tags

27 Dec 2012, 03:07
2
KUDOS
1
This post was
BOOKMARKED
smartmanav wrote:
Can't we do this question using unitary method ?

Hi Smartmanav,

I guess this cannot be done by Unitary method as we are given the Constant rate of A i.e 25L/min. Now does it tell you the time A will take alone to fill the tank. No, because we do not the volume/size of the tank.

That is why method suggested by Bunuel of Rate*Time =Work

Thanks
Mridul
_________________

“If you can't fly then run, if you can't run then walk, if you can't walk then crawl, but whatever you do you have to keep moving forward.”

Kudos [?]: 847 [2], given: 724

Manager
Joined: 22 Oct 2009
Posts: 242

Kudos [?]: 95 [1], given: 1

GMAT 1: 760 Q49 V44
GPA: 3.88
Re: Data sufficiency work rate problem [#permalink]

### Show Tags

15 Jul 2010, 17:18
1
KUDOS
3
This post was
BOOKMARKED
ksharma12 wrote:
15. working together at their constant rates , A and B can fill an empty tank to capacity in1/2 hr.what is the constant rate of pump B?
1) A's constant rate is 25LTS / min
2) the tanks capacity is 1200 lts.

Can someone solve this beyond just showing what is sufficient?

I know the answer is A but I need to know how to solve to fully grasp the concept of only needing the first statement.

Thank you

Question: If A and B can fill 2 tanks in 1 hour together, then how many tanks can B fill up in 1 hour alone?

I'm setting this up as ratios of "x tanks per 1 hour" :
$$\frac{a}{1hr}+\frac{b}{1hr}= \frac{2}{1hr}$$

1) This does NOT give you "a" because you need to know the size of the tanks. As we stated above, the ratios above show how many TANKS per hour each can fill, not how many gallons or liters. NOT sufficient

2) This gives you the tank's capacity, which is valuable in combination with 1). However, just knowing the tank's volume isn't useful since we don't know the flow rate of A. NOT sufficient

Now that we have both the flow rate and the volume of the tank, we can easily find the value of "a" in the above equation. Both statements together are sufficient.

Are you sure the answer is A? I definitely think it is C. Where is this question from?

Kudos [?]: 95 [1], given: 1

Manager
Joined: 03 Feb 2010
Posts: 68

Kudos [?]: 149 [1], given: 4

Re: Data sufficiency work rate problem [#permalink]

### Show Tags

15 Jul 2010, 17:31
1
KUDOS
Yea i thought it was c too.

but its not.

This question is from the work/rate made easy thread in the beginning of the quant forum.

I figured knowing the rate per minute was not sufficient unless we knew the total.

Kudos [?]: 149 [1], given: 4

Manager
Joined: 22 Oct 2009
Posts: 242

Kudos [?]: 95 [1], given: 1

GMAT 1: 760 Q49 V44
GPA: 3.88
Re: Data sufficiency work rate problem [#permalink]

### Show Tags

15 Jul 2010, 17:57
1
KUDOS
I'm definitely agreeing with you here. Must be a typo -- or we're both missing something obvious!

Kudos [?]: 95 [1], given: 1

Manager
Joined: 03 Jun 2010
Posts: 172

Kudos [?]: 71 [1], given: 40

Location: United States (MI)
Concentration: Marketing, General Management
Re: Data sufficiency work rate problem [#permalink]

### Show Tags

16 Jul 2010, 02:08
1
KUDOS
(1/A+1/B)*0.5=1
It means that the work is done by 2 employees.
From (1) we have A, so we can solve for B.
That's all.
(A)

Kudos [?]: 71 [1], given: 40

Intern
Joined: 18 Jun 2012
Posts: 38

Kudos [?]: 9 [1], given: 15

Re: working together at their constant rates , A and B can fill [#permalink]

### Show Tags

25 Oct 2012, 07:25
1
KUDOS
Can't we do this question using unitary method ?

Kudos [?]: 9 [1], given: 15

Manager
Joined: 07 May 2013
Posts: 108

Kudos [?]: 30 [1], given: 1

Re: Working together at their constant rates, A and B can fill [#permalink]

### Show Tags

29 Aug 2013, 18:13
1
KUDOS
1
This post was
BOOKMARKED
The standard formula for solving this problem is AB/A+B=1/2 hrs
we need A to get to B, where A is the time taken by Pipe A to fill ENTIRE tank alone
from options the time taken by Pipe A to fill ENTIRE tank alone=1200/25=48 minutes
substitute in equation above to get value of B. SIMPLE!

Kudos [?]: 30 [1], given: 1

Intern
Joined: 21 Apr 2014
Posts: 40

Kudos [?]: 27 [1], given: 0

Re: Working together at their constant rates, A and B can fill [#permalink]

### Show Tags

14 Oct 2014, 08:39
1
KUDOS
1
This post was
BOOKMARKED
So let's put this into an equation. We know that (Arate+Brate)30min=T, if T= the tank's capacity.

(1) now we know that Arate=25lirer/min, so we can plug that into the equation and we get (25lit/min+Brate)30min=T

This is not sufficient, because there are still too many unkowns. For example, it T=900 liters then Brate would equal 5 liters/min. But if T=9,000 then Brate would equal 275 liters/min

(2) now we know that T= 1200 liters, plugging that into the equation we get (Arate+Brate)30min=1200 liters

This is also not sufficient, because there are a variety of different combinations of Arate and Brate that can fit this equation. For example, Arate could be 10 liters per min and Brate could be 30 liters per min OR vice versa.

Now lets try them both together by plugging (1) and (2) into the equation:

(25lit/min+Brate)30min=1200 liters

divide both sides by 30 min and we get: 25 liters/min+Brate=40liters/min

that means Brate equals 15 liters, so the answer is (C) both together are sufficient

In the actual GMAT, you would not need to go so far as to figure out exactly what B rate. That would be a waste of time. As soon as you know what you CAN solve it with both, which can be determined by the fact that there is only 1 unknown then you should select C and move on.
_________________

Eliza
GMAT Tutor
bestgmatprepcourse.com

Kudos [?]: 27 [1], given: 0

GMAT Club Legend
Joined: 09 Sep 2013
Posts: 16636

Kudos [?]: 273 [0], given: 0

Re: Working together at their constant rates, A and B can fill [#permalink]

### Show Tags

14 Oct 2014, 03:22
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

Kudos [?]: 273 [0], given: 0

GMAT Club Legend
Joined: 09 Sep 2013
Posts: 16636

Kudos [?]: 273 [0], given: 0

Re: Working together at their constant rates, A and B can fill [#permalink]

### Show Tags

27 Oct 2015, 12:07
Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________

Kudos [?]: 273 [0], given: 0

Director
Joined: 04 Jun 2016
Posts: 647

Kudos [?]: 367 [0], given: 36

GMAT 1: 750 Q49 V43
Re: Working together at their constant rates, A and B can fill [#permalink]

### Show Tags

01 Aug 2016, 06:59
ksharma12 wrote:
Working together at their constant rates, A and B can fill an empty tank to capacity in 1/2 hours. What is the constant rate of pump B?

(1) A's constant rate is 25 LTS / min
(2) The tanks capacity is 1200 lts.

ksharma12 wrote:
Working together at their constant rates, A and B can fill an empty tank to capacity in 1/2 hours. What is the constant rate of pump B?

(1) A's constant rate is 25 LTS / min
(2) The tanks capacity is 1200 lts.

Let the rate of A be a and the rate of B be b

(1) A's constant rate is 25 LTS / min
(a+b)time = Volume of tank
(25+b)*30 minutes = Volume of tank
750+30b = volume of tank
Rate of B and the volume of tank is not known
INSUFFICIENT

(2) The tanks capacity is 1200 lts.
(a+b)*time = 1200
(a+b)*30 minutes = 1200
30a+30b=1200
Rate of A and rate of B is not known
INSUFFICIENT

MERGE BOTH
750 + 30b= 30a+30b {since both equations are equal to 1200}
30a=750
a=750/30 = 25

Now rate of A is known. Rate of B can be easily calculated by putting value of in any equation
for example 30a+30b =1200
750+30b=1200
30b=450
b= 15

SUFFICIENT

we need both statements together

_________________

Posting an answer without an explanation is "GOD COMPLEX". The world doesn't need any more gods. Please explain you answers properly.
FINAL GOODBYE :- 17th SEPTEMBER 2016. .. 16 March 2017 - I am back but for all purposes please consider me semi-retired.

Kudos [?]: 367 [0], given: 36

VP
Status: Learning
Joined: 20 Dec 2015
Posts: 1070

Kudos [?]: 69 [0], given: 533

Location: India
Concentration: Operations, Marketing
GMAT 1: 670 Q48 V36
GRE 1: 314 Q157 V157
GPA: 3.4
WE: Manufacturing and Production (Manufacturing)
Re: Working together at their constant rates, A and B can fill [#permalink]

### Show Tags

20 Jun 2017, 20:47
Imo C
At first sight the answer seems to be statement 1 but on closer inspection we come to know about its flaw as the rate is given in 25 liters per minute and from the question stem we have been given only the completion time ,So we need the capacity of the tank .
_________________

We are more often frightened than hurt; and we suffer more from imagination than from reality

Kudos [?]: 69 [0], given: 533

Re: Working together at their constant rates, A and B can fill   [#permalink] 20 Jun 2017, 20:47
Display posts from previous: Sort by