It is currently 21 Apr 2018, 02:56

### 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

# One water pump can fill half of a certain empty tank in 3 hours. Anoth

Author Message
TAGS:

### Hide Tags

Intern
Joined: 16 Oct 2011
Posts: 7
Location: Japan
GMAT Date: 03-29-2012
WE: Consulting (Consulting)
One water pump can fill half of a certain empty tank in 3 hours. Anoth [#permalink]

### Show Tags

04 Jan 2012, 10:17
1
KUDOS
7
This post was
BOOKMARKED
00:00

Difficulty:

25% (medium)

Question Stats:

70% (01:19) correct 30% (01:37) wrong based on 501 sessions

### HideShow timer Statistics

One water pump can fill half of a certain empty tank in 3 hours. Another pump can fill half of the same tank in $$3\frac{1}{2}$$ hours. Working together, how long will it take these two pumps to fill the entire tank?

(A) $$1\frac{7}{13}$$

(B) $$1\frac{5}{8}$$

(C) $$3\frac{1}{4}$$

(D) $$3\frac{3}{13}$$

(E) $$3\frac{1}{2}$$
[Reveal] Spoiler: OA
Manager
Status: MBA Aspirant
Joined: 12 Jun 2010
Posts: 151
Location: India
WE: Information Technology (Investment Banking)
Re: One water pump can fill half of a certain empty tank in 3 hours. Anoth [#permalink]

### Show Tags

04 Jan 2012, 10:59
1
This post was
BOOKMARKED
36mba wrote:
One water pump can fill half of a certain empty tank in 3 hours. Another pump can fill half of the same tank in $$3\frac{1}{2}$$ hours. Working together, how long will it take these two pumps to fill the entire tank?

(A) $$1\frac{7}{13}$$
(B) $$1\frac{5}{8}$$
(C) $$3\frac{1}{4}$$
(D) $$3\frac{3}{13}$$
(E) $$3\frac{1}{2}$$

One pump can fill a tank in 3 hours and another in 3.5 hours
so the rate at which both can half fill the tank is (1/3+1/3.5) => 13/21

Thus half of the tank can be filled in 21/13

so for filling the complete tank => 21/13*2 = 42/13 (D)
Senior Manager
Joined: 13 May 2011
Posts: 276
WE 1: IT 1 Yr
WE 2: Supply Chain 5 Yrs
Re: One water pump can fill half of a certain empty tank in 3 hours. Anoth [#permalink]

### Show Tags

04 Jan 2012, 11:02
1st pump takes (3+3)=6 hours to fill the full tank
2nd pump takes (3.5+3.5)=7 hours to fill the full tank
Therefore, 1/6 + 1/7= 1/T [T= time it will take if they work together to fill the tank]
solving for T= 3 3/13=D
Manager
Joined: 29 Jul 2011
Posts: 99
Location: United States
Re: One water pump can fill half of a certain empty tank in 3 hours. Anoth [#permalink]

### Show Tags

04 Jan 2012, 11:45
2
This post was
BOOKMARKED
1st pump, 1/2 tank -> 3 hours, full -> 6 hours. This implies rate of 1/6 tank/hr
2nd pump, 1/2 tank -> 3.5 hours, full -> 7 hours. This implies rate of 1/7 tank/hr

Combined rate 1/6 + 1/7 = 13/42
For full tank -> 1/(13/42) = 42/13 = 3 3/13 -> D
_________________

I am the master of my fate. I am the captain of my soul.
Please consider giving +1 Kudos if deserved!

DS - If negative answer only, still sufficient. No need to find exact solution.
PS - Always look at the answers first
CR - Read the question stem first, hunt for conclusion
SC - Meaning first, Grammar second
RC - Mentally connect paragraphs as you proceed. Short = 2min, Long = 3-4 min

Intern
Joined: 23 Dec 2014
Posts: 48
Re: One water pump can fill half of a certain empty tank in 3 hours. Anoth [#permalink]

### Show Tags

16 Feb 2015, 12:20
36mba wrote:
One water pump can fill half of a certain empty tank in 3 hours. Another pump can fill half of the same tank in $$3\frac{1}{2}$$ hours. Working together, how long will it take these two pumps to fill the entire tank?

(A) $$1\frac{7}{13}$$

(B) $$1\frac{5}{8}$$

(C) $$3\frac{1}{4}$$

(D) $$3\frac{3}{13}$$

(E) $$3\frac{1}{2}$$

1/A = .5/3

1/B = .5/ 3.5

1/A+1/B = .5/3+.5/3.5 = 1/6+1/7 = 13/42

so rate is 13/42
Work =1
Time = 1/ (13/42) = 42/13
EMPOWERgmat Instructor
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 11492
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: 340 Q170 V170
Re: One water pump can fill half of a certain empty tank in 3 hours. Anoth [#permalink]

### Show Tags

16 Feb 2015, 19:01
1
KUDOS
Expert's post
1
This post was
BOOKMARKED
Hi All,

This question is an example of a "Work Formula" question; since it involves just two entities (in this case, water pumps), we can us the Work Formula to quickly get to the correct answer.

We're told that 2 different water pumps can fill HALF of a tank in 3 hours and 3.5 hours, respectively. That means that the two pumps could fill the ENTIRE tank in 6 hours and 7 hours, respectively.

Work = (A)(B)/(A+B)

A = 6 hours
B = 7 hours

(6)(7)/(6+7) = 42/13 = 3 3/13 hours to fill the entire tank when working together.

[Reveal] Spoiler:
D

GMAT assassins aren't born, they're made,
Rich
_________________

760+: Learn What GMAT Assassins Do to Score at the Highest Levels
Contact Rich at: Rich.C@empowergmat.com

# Rich Cohen

Co-Founder & GMAT Assassin

Special Offer: Save \$75 + GMAT Club Tests Free
Official GMAT Exam Packs + 70 Pt. Improvement Guarantee
www.empowergmat.com/

***********************Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!***********************

Manager
Joined: 20 Jan 2017
Posts: 61
Location: United States (NY)
Schools: CBS '20 (A)
GMAT 1: 750 Q48 V44
GMAT 2: 610 Q34 V41
GPA: 3.92
Re: One water pump can fill half of a certain empty tank in 3 hours. Anoth [#permalink]

### Show Tags

30 Jan 2017, 04:05
1) First we need to find the rates of each pump individually: $$r*t=w, r1*3=1/2, r1=1/2*1/3=1/6; r2*7/2=1/2, r2=1/2*2/7=1/7$$.
2) Then we need to combine the two rates, since the pumps are working simultaneously: $$1/6+1/7=13/42$$
3) Now we can find the time it takes the two of them to fill the tank: $$13/42*T=1$$; $$T=42/13=3 \frac{3}{13}$$
Target Test Prep Representative
Affiliations: Target Test Prep
Joined: 04 Mar 2011
Posts: 2273
Re: One water pump can fill half of a certain empty tank in 3 hours. Anoth [#permalink]

### Show Tags

02 Feb 2017, 12:07
1
KUDOS
Expert's post
1
This post was
BOOKMARKED
36mba wrote:
One water pump can fill half of a certain empty tank in 3 hours. Another pump can fill half of the same tank in $$3\frac{1}{2}$$ hours. Working together, how long will it take these two pumps to fill the entire tank?

(A) $$1\frac{7}{13}$$

(B) $$1\frac{5}{8}$$

(C) $$3\frac{1}{4}$$

(D) $$3\frac{3}{13}$$

(E) $$3\frac{1}{2}$$

We are given that a water pump can fill half of a certain tank in 3 hours; thus, the rate of the pump is (1/2)/3 = 1/6. We are given that another pump can fill 1/2 of the same tank in 3½, or 7/2, hours. Thus, the rate of the second pump is (1/2)/(7/2) = 2/14 = 1/7. If we let t = the time it takes the two pumps working together to fill the entire tank, and if we let 1 equal the work (i.e., filling the entire tank) needed to be completed, we can create the following equation and determine t:

(1/6)t + (1/7)t = 1

Multiplying the entire equation by 42, we have:

7t + 6t = 42

13t = 42

t = 42/13 = 3 3/13

_________________

Jeffery Miller

GMAT Quant Self-Study Course
500+ lessons 3000+ practice problems 800+ HD solutions

Re: One water pump can fill half of a certain empty tank in 3 hours. Anoth   [#permalink] 02 Feb 2017, 12:07
Display posts from previous: Sort by