GMAT Question of the Day: Daily via email | Daily via Instagram New to GMAT Club? Watch this Video

It is currently 03 Jun 2020, 20:48

Close

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
Your Progress

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

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Close

Request Expert Reply

Confirm Cancel

A water tank is fitted with 8 pipes, some of these 8 pipes fill the

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:

Hide Tags

Find Similar Topics 
General GMAT Forum Moderator
User avatar
V
Joined: 15 Jan 2018
Posts: 909
Concentration: General Management, Finance
GMAT 1: 720 Q50 V37
Reviews Badge CAT Tests
A water tank is fitted with 8 pipes, some of these 8 pipes fill the  [#permalink]

Show Tags

New post 08 Aug 2019, 11:10
1
1
18
00:00
A
B
C
D
E

Difficulty:

  65% (hard)

Question Stats:

63% (02:43) correct 37% (02:50) wrong based on 169 sessions

HideShow timer Statistics

A water tank is fitted with 8 pipes, some of these 8 pipes fill the tank and others empty the tank. Each of the pipes that fills the tank fills it in 8 hours, while each of the pipes that empties the tank empties it in 6 hours. If all the 8 pipes are kept open when the water tank is full, it takes 6 hours to drain the tank. How many of these 8 pipes fill the tank?

1. 2 pipes
2. 4 pipes
3. 5 pipes
4. 6 pipes
5. 8 pipes

_________________
General GMAT Forum Senior Moderator | D-Day: June 27, 2020

New to GMAT Club? Start with the study plan!
Should I retake GMAT? Retaking GMAT Strategies!

What Are My Chances - Automated Profile Evaluation Tool is Here!
DS Forum Moderator
User avatar
V
Joined: 19 Oct 2018
Posts: 1879
Location: India
Premium Member
A water tank is fitted with 8 pipes, some of these 8 pipes fill the  [#permalink]

Show Tags

New post 08 Aug 2019, 11:57
3
Assume the capacity of tank= LCM(6,8)=24units
Inlet pipe can fill 24/8= 3 units every hour.
Outlet pipe can discharge 24/6= 4 units every hour.

Total number of inlet pipes=x
Total number of outlet pipes= 8-x

{(8-x)*4 - 3x}*6= 24
32-4x-3x= 4
x=4

Total number of inlet pipes=4


DisciplinedPrep wrote:
A water tank is fitted with 8 pipes, some of these 8 pipes fill the tank and others empty the tank. Each of the pipes that fills the tank fills it in 8 hours, while each of the pipes that empties the tank empties it in 6 hours. If all the 8 pipes are kept open when the water tank is full, it takes 6 hours to drain the tank. How many of these 8 pipes fill the tank?

1. 2 pipes
2. 4 pipes
3. 5 pipes
4. 6 pipes
5. 8 pipes
Intern
Intern
avatar
B
Joined: 21 Nov 2018
Posts: 17
Location: Nigeria
Concentration: Finance, Entrepreneurship
GPA: 4
WE: Analyst (Investment Banking)
Re: A water tank is fitted with 8 pipes, some of these 8 pipes fill the  [#permalink]

Show Tags

New post 07 Sep 2019, 03:40
1
Bunuel can you explain this please?
VP
VP
avatar
D
Joined: 07 Dec 2014
Posts: 1253
A water tank is fitted with 8 pipes, some of these 8 pipes fill the  [#permalink]

Show Tags

New post 07 Sep 2019, 20:12
DisciplinedPrep wrote:
A water tank is fitted with 8 pipes, some of these 8 pipes fill the tank and others empty the tank. Each of the pipes that fills the tank fills it in 8 hours, while each of the pipes that empties the tank empties it in 6 hours. If all the 8 pipes are kept open when the water tank is full, it takes 6 hours to drain the tank. How many of these 8 pipes fill the tank?

1. 2 pipes
2. 4 pipes
3. 5 pipes
4. 6 pipes
5. 8 pipes


let x=number of pipes filling tank
6[(8-x)(1/6)-(x)(1/8)]=1→
x=4
Intern
Intern
avatar
B
Joined: 01 Jul 2018
Posts: 2
A water tank is fitted with 8 pipes, some of these 8 pipes fill the  [#permalink]

Show Tags

New post 19 Sep 2019, 10:13
Let x be the no. of pipes that fill the tank. Hence, no. of pipes that empty the tank will be (8-x).
Rate of pipes that fill is 1/8 and rate of pipes that empty the tank is 1/6.

We are given the information that the tank gets emptied in 6 hrs. Rate of tank emptying per hour is 1/6.
Let's form an equation from the above information.

\(1/6*(8-x)- 1/8*(x) = 1/6\)
\(8/6 - x/6 - x/8 = 1/6\)
\(x/6 - x/8 = 1/6 - 8/6\)
\(-14x/48 = -7/6\)
\(-7x/24 = -7/6\)

Solving for x gives, x =4.

Hence, no. of pipes that fill the tank is 4
GMAT Club Legend
GMAT Club Legend
User avatar
V
Joined: 18 Aug 2017
Posts: 6305
Location: India
Concentration: Sustainability, Marketing
GPA: 4
WE: Marketing (Energy and Utilities)
GMAT ToolKit User Reviews Badge CAT Tests
Re: A water tank is fitted with 8 pipes, some of these 8 pipes fill the  [#permalink]

Show Tags

New post 24 Sep 2019, 02:08
given
total pipes = 8
rate of inlet = 1/8
rate of outlet = 1/6
let total volume of tank be 24 ltrs
so rate of filling ; 24/8 ; 3 ltrs/hr and rate of draining ; 24/6 ; 4 ltrs/hr
work done ; rate * time
work = 24
time of drain is 6 hrs
24= (3*a-(4*(8-a)) ) *6
solve for a = 4
IMO B

DisciplinedPrep wrote:
A water tank is fitted with 8 pipes, some of these 8 pipes fill the tank and others empty the tank. Each of the pipes that fills the tank fills it in 8 hours, while each of the pipes that empties the tank empties it in 6 hours. If all the 8 pipes are kept open when the water tank is full, it takes 6 hours to drain the tank. How many of these 8 pipes fill the tank?

1. 2 pipes
2. 4 pipes
3. 5 pipes
4. 6 pipes
5. 8 pipes
Target Test Prep Representative
User avatar
V
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 10651
Location: United States (CA)
Re: A water tank is fitted with 8 pipes, some of these 8 pipes fill the  [#permalink]

Show Tags

New post 24 Sep 2019, 10:26
DisciplinedPrep wrote:
A water tank is fitted with 8 pipes, some of these 8 pipes fill the tank and others empty the tank. Each of the pipes that fills the tank fills it in 8 hours, while each of the pipes that empties the tank empties it in 6 hours. If all the 8 pipes are kept open when the water tank is full, it takes 6 hours to drain the tank. How many of these 8 pipes fill the tank?

1. 2 pipes
2. 4 pipes
3. 5 pipes
4. 6 pipes
5. 8 pipes


We can let the number of filling pipes be n, and thus the number of emptying pipes = 8 - n. Since the rate of each filling pipe is ⅛ and that of each emptying pipe is -⅙ and the combined rate of all pipes is -⅙, we can create the equation:

n x ⅛ + (8 - n) x -⅙ = -⅙

Multiplying by 24, we have:

3n - 4(8 - n) = -4

3n - 32 + 4n = -4

7n = 28

n = 4

Answer: B/2
_________________

Scott Woodbury-Stewart

Founder and CEO

Scott@TargetTestPrep.com
TTP - Target Test Prep Logo
202 Reviews

5-star rated online GMAT quant
self study course

See why Target Test Prep is the top rated GMAT quant course on GMAT Club. Read Our Reviews

If you find one of my posts helpful, please take a moment to click on the "Kudos" button.

SVP
SVP
avatar
D
Joined: 24 Nov 2016
Posts: 1578
Location: United States
Re: A water tank is fitted with 8 pipes, some of these 8 pipes fill the  [#permalink]

Show Tags

New post 09 Oct 2019, 05:09
DisciplinedPrep wrote:
A water tank is fitted with 8 pipes, some of these 8 pipes fill the tank and others empty the tank. Each of the pipes that fills the tank fills it in 8 hours, while each of the pipes that empties the tank empties it in 6 hours. If all the 8 pipes are kept open when the water tank is full, it takes 6 hours to drain the tank. How many of these 8 pipes fill the tank?

1. 2 pipes
2. 4 pipes
3. 5 pipes
4. 6 pipes
5. 8 pipes


rate*time=distance

pipes: x+y=8… y=8-x

in rate: 1/8
out rate: 1/6

\(\frac{1}{x(1/8)-y(1/6)}=-6…\frac{1}{x/8-(8-x/6)}=-6…\frac{1}{(6x-64+8x)/48}=-6…48=384-84x…x,y=4\)

Answer (B)
Manager
Manager
avatar
B
Joined: 10 Nov 2018
Posts: 83
Re: A water tank is fitted with 8 pipes, some of these 8 pipes fill the  [#permalink]

Show Tags

New post 24 Oct 2019, 04:16
ScottTargetTestPrep sir how did you arrive at the combined rate of -1/6?
Target Test Prep Representative
User avatar
V
Status: Founder & CEO
Affiliations: Target Test Prep
Joined: 14 Oct 2015
Posts: 10651
Location: United States (CA)
Re: A water tank is fitted with 8 pipes, some of these 8 pipes fill the  [#permalink]

Show Tags

New post 25 Oct 2019, 09:38
1
rocky620 wrote:
ScottTargetTestPrep sir how did you arrive at the combined rate of -1/6?


From the sentence "If all the 8 pipes are kept open when the water tank is full, it takes 6 hours to drain the tank.", we understand that when all the pipes are combined, 1/6 of the tank is emptied in one hour. Since the tank is being emptied instead of being filled, the combined rate will be negative. That's how we find the combined rate of -1/6.
_________________

Scott Woodbury-Stewart

Founder and CEO

Scott@TargetTestPrep.com
TTP - Target Test Prep Logo
202 Reviews

5-star rated online GMAT quant
self study course

See why Target Test Prep is the top rated GMAT quant course on GMAT Club. Read Our Reviews

If you find one of my posts helpful, please take a moment to click on the "Kudos" button.

Manager
Manager
avatar
B
Joined: 10 Nov 2018
Posts: 83
Re: A water tank is fitted with 8 pipes, some of these 8 pipes fill the  [#permalink]

Show Tags

New post 29 Oct 2019, 21:48
ScottTargetTestPrep got it sir, thanks.
Senior Manager
Senior Manager
User avatar
P
Status: So far only Dreams i have!!
Joined: 05 Jan 2015
Posts: 305
WE: Consulting (Computer Software)
Premium Member Reviews Badge
Re: A water tank is fitted with 8 pipes, some of these 8 pipes fill the  [#permalink]

Show Tags

New post 30 Oct 2019, 08:52
Assume capacity of tank be LCM of 6 and 8 = 24L
Now,
- Per hour rate at inlet of tank = 24/8 = 3L
- Per hour rate at outlet of tank = 24/6 = 4L

if both pipes are open together, -1L is per hour decrease in quantity of tank. but given is that tank will get emptied in 6 hours -- means per hour rate should be -4L.

From above we can deduce that if 4 Inlet and 4 outlet pipes are open - tank will get emptied in 6 hours.

Answer - Option B!
_________________
Unable to Give Up!
GMAT Club Bot
Re: A water tank is fitted with 8 pipes, some of these 8 pipes fill the   [#permalink] 30 Oct 2019, 08:52

A water tank is fitted with 8 pipes, some of these 8 pipes fill the

  new topic post reply Question banks Downloads My Bookmarks Reviews Important topics  





cron

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne