GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 20 Feb 2019, 14:25

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
Events & Promotions in February
PrevNext
SuMoTuWeThFrSa
272829303112
3456789
10111213141516
17181920212223
242526272812
Open Detailed Calendar
  • Free GMAT Prep Hour

     February 20, 2019

     February 20, 2019

     08:00 PM EST

     09:00 PM EST

    Strategies and techniques for approaching featured GMAT topics. Wednesday, February 20th at 8 PM EST
  • Online GMAT boot camp for FREE

     February 21, 2019

     February 21, 2019

     10:00 PM PST

     11:00 PM PST

    Kick off your 2019 GMAT prep with a free 7-day boot camp that includes free online lessons, webinars, and a full GMAT course access. Limited for the first 99 registrants! Feb. 21st until the 27th.

Machine A can do a job in 24 hours at a constant rate and machine A do

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

Hide Tags

 
Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6967
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Machine A can do a job in 24 hours at a constant rate and machine A do  [#permalink]

Show Tags

New post Updated on: 13 Mar 2016, 05:10
1
7
00:00
A
B
C
D
E

Difficulty:

  15% (low)

Question Stats:

78% (01:42) correct 22% (02:02) wrong based on 226 sessions

HideShow timer Statistics

Machine A can do a job in 24 hours at a constant rate. If Machine A does the job for 8 hours and Machine B does the rest of the job, which works at 2/3 constant rate of Machine A. How long will it take for Machine B alone to do the rest of the job?

A. 12hrs
B. 16hrs
C. 24hrs
D. 28hrs
E. 32hrs


* A solution will be posted in two days.

_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"


Originally posted by MathRevolution on 11 Mar 2016, 05:04.
Last edited by MathRevolution on 13 Mar 2016, 05:10, edited 3 times in total.
Math Expert
User avatar
V
Joined: 02 Aug 2009
Posts: 7334
Premium Member Reviews Badge
Re: Machine A can do a job in 24 hours at a constant rate and machine A do  [#permalink]

Show Tags

New post 11 Mar 2016, 05:35
MathRevolution wrote:
Machine A can do a job in 24 hours at a constant rate and machine A do the job in 8 hours. Machine B can do the same job at a 2/3 constant rate of machine A. If machine B does the rest job, what is the amount of hours done by machine B alone?

A. 12hrs
B. 16hrs
C. 24hrs
D. 28hrs
E. 32hrs


* A solution will be posted in two days.

Hi,

The Q does not seem to be properly framed..
I believe it should be--

Machine A can do a job in 24 hours at a constant rate and machine A does the job alone for 8 hours. Machine B can do the same job at a 2/3 constant rate of machine A. If machine B does the rest job, what is the amount of hours done by machine B alone?


solution


machine A will do 8/24 in 8 hrs, so A does 1/3 of the work ..
Therefore, B will do the remaining 2/3 rd work alone..
As the speed of B is 2/3 rate of A, B will do the 2/3rd work in same time that A takes to complete full job...
ans 24
C

_________________

1) Absolute modulus : http://gmatclub.com/forum/absolute-modulus-a-better-understanding-210849.html#p1622372
2)Combination of similar and dissimilar things : http://gmatclub.com/forum/topic215915.html
3) effects of arithmetic operations : https://gmatclub.com/forum/effects-of-arithmetic-operations-on-fractions-269413.html
4) Base while finding % increase and % decrease : https://gmatclub.com/forum/percentage-increase-decrease-what-should-be-the-denominator-287528.html


GMAT Expert

Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6967
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Re: Machine A can do a job in 24 hours at a constant rate and machine A do  [#permalink]

Show Tags

New post 13 Mar 2016, 05:11
Sorry for the confusion. I have revised the question.
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Math Revolution GMAT Instructor
User avatar
V
Joined: 16 Aug 2015
Posts: 6967
GMAT 1: 760 Q51 V42
GPA: 3.82
Premium Member
Re: Machine A can do a job in 24 hours at a constant rate and machine A do  [#permalink]

Show Tags

New post 13 Mar 2016, 21:16
Machine A can do a job in 24 hours at a constant rate. If Machine A does the job for 8 hours and Machine B does the rest of the job, which works at 2/3 constant rate of Machine A. How long will it take for Machine B alone to do the rest of the job?

A. 12hrs
B. 16hrs
C. 24hrs
D. 28hrs
E. 32hrs


Power of Machine A=W/24hrs. Since Machine A does the job for 8 hours, which becomes (W/3)/8hrs and 2W/3 is left. However, as power of Machine B is 2/3 of Machine A, power of B is (2/3)(W/24hrs)=(2W/3)/24hrs. Eventually, it takes 24 hours for Machine B to do the rest of the job.
_________________

MathRevolution: Finish GMAT Quant Section with 10 minutes to spare
The one-and-only World’s First Variable Approach for DS and IVY Approach for PS with ease, speed and accuracy.
"Only $149 for 3 month Online Course"
"Free Resources-30 day online access & Diagnostic Test"
"Unlimited Access to over 120 free video lessons - try it yourself"

Manager
Manager
avatar
Joined: 09 Jun 2015
Posts: 92
Re: Machine A can do a job in 24 hours at a constant rate and machine A do  [#permalink]

Show Tags

New post 13 Mar 2016, 21:24
1
MathRevolution wrote:
Machine A can do a job in 24 hours at a constant rate. If Machine A does the job for 8 hours and Machine B does the rest of the job, which works at 2/3 constant rate of Machine A. How long will it take for Machine B alone to do the rest of the job?

A. 12hrs
B. 16hrs
C. 24hrs
D. 28hrs
E. 32hrs


* A solution will be posted in two days.

In 8 hours A can complete one third work. The remaining work is two thirds.
B performs two third of the efficiency of A; So B takes 36 hours to complete the full task.
Now B has to do only two thirds of the work. Therefore, two thirds of 36 hours = 24 hours.
Director
Director
User avatar
S
Joined: 17 Dec 2012
Posts: 624
Location: India
Machine A can do a job in 24 hours at a constant rate and machine A do  [#permalink]

Show Tags

New post 13 Mar 2016, 21:44
MathRevolution wrote:
Machine A can do a job in 24 hours at a constant rate. If Machine A does the job for 8 hours and Machine B does the rest of the job, which works at 2/3 constant rate of Machine A. How long will it take for Machine B alone to do the rest of the job?

A. 12hrs
B. 16hrs
C. 24hrs
D. 28hrs
E. 32hrs


* A solution will be posted in two days.

We can equate work done as follows:
8/24 + x/36 = 1

x/36=2/3
x=24 hrs
_________________

Srinivasan Vaidyaraman
Sravna Holistic Solutions
http://www.sravnatestprep.com

Holistic and Systematic Approach

Intern
Intern
User avatar
B
Joined: 28 May 2017
Posts: 18
Re: Machine A can do a job in 24 hours at a constant rate and machine A do  [#permalink]

Show Tags

New post 25 Aug 2017, 08:05
Ans c 24 hours
Given
A takes 24 hours
And

The machine b is 2/3 as consistent as a

So time taken by it would be 3/2 as A

A works for 8 hours so 8/24 = 1/3 work is done

Remaining work = 1-1/3= 2/3

A completed 1/3 of work in 8 hours and b would take 3/2 as time as A so
A would complete the same work in 3/2*8= 12 hours

So 1/3 of work is completed by b in 12 hours
So 2/3 will be done in 24 hours

Hope it helps
Peace


Sent from my iPhone using GMAT Club Forum mobile app
Senior SC Moderator
avatar
V
Joined: 22 May 2016
Posts: 2489
Machine A can do a job in 24 hours at a constant rate and machine A do  [#permalink]

Show Tags

New post 26 Aug 2017, 11:40
2
1
MathRevolution wrote:
Machine A can do a job in 24 hours at a constant rate. If Machine A does the job for 8 hours and Machine B does the rest of the job, which works at 2/3 constant rate of Machine A. How long will it take for Machine B alone to do the rest of the job?

A. 12hrs
B. 16hrs
C. 24hrs
D. 28hrs
E. 32hrs

* A solution will be posted in two days.

A's rate = \(\frac{1}{24}\)

B's rate is \(\frac{2}{3}\) (of) A:

\(\frac{1}{24}\) * \(\frac{2}{3}\) = \(\frac{1}{36}\) = B's rate

Amount of work for B? A works for 8 hours. \((\frac{1}{24})\) * 8 = \(\frac{1}{3}\) of the work is finished.

1 - \(\frac{1}{3}\) = \(\frac{2}{3}\) of work remains.

Time for B to finish? B has to finish remaining \(\frac{2}{3}\) of work. At B's rate, W/r = t, that will take

\(\frac{\frac{2}{3}}{\frac{1}{36}}\) =

\(\frac{2}{3}\) * 36 = 24 hours

Answer C
_________________

To live is the rarest thing in the world.
Most people just exist.

Oscar Wilde

Senior PS Moderator
User avatar
V
Joined: 26 Feb 2016
Posts: 3340
Location: India
GPA: 3.12
Premium Member
Machine A can do a job in 24 hours at a constant rate and machine A do  [#permalink]

Show Tags

New post 27 Aug 2017, 20:09
1
1
Since Machine A does a job in 24 hours,
lets assume the number of units of work done to be a multiple of 24(for eg, 72 units)
So the rate of Machine A doing the work is 3 units/hour

It has been given that B does the work at \(\frac{2}{3}\)rd the rate of A.
Therefore Machine B does the work at the rate of 2 units/hour

Since Machine A does the work for 8 hours,
Machine B does the rest of the work for x days till the work is complete.

8*3 + x*2 = 72(total units of work)
2x = 48
x = 24
Therefore, Machine B takes 24 hours to complete the remaining work(Option C)
_________________

You've got what it takes, but it will take everything you've got

Target Test Prep Representative
User avatar
G
Status: Head GMAT Instructor
Affiliations: Target Test Prep
Joined: 04 Mar 2011
Posts: 2827
Re: Machine A can do a job in 24 hours at a constant rate and machine A do  [#permalink]

Show Tags

New post 31 Aug 2017, 09:22
1
MathRevolution wrote:
Machine A can do a job in 24 hours at a constant rate. If Machine A does the job for 8 hours and Machine B does the rest of the job, which works at 2/3 constant rate of Machine A. How long will it take for Machine B alone to do the rest of the job?

A. 12hrs
B. 16hrs
C. 24hrs
D. 28hrs
E. 32hrs


The rate of machine A is 1/24, so in 8 hours 1/3 of the job is completed, and thus 2/3 of the job is left to be completed.

If the rate of machine B is 2/3 that of machine A, then the rate of machine B is (2/3)(1/24) = 1/36.

Thus, it will take machine B (2/3)/(1/36) = 2/3 x 36 = 24 hours to complete the rest of the job.

Answer: C
_________________

Jeffery Miller
Head of GMAT Instruction

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

VP
VP
avatar
P
Joined: 07 Dec 2014
Posts: 1153
Re: Machine A can do a job in 24 hours at a constant rate and machine A do  [#permalink]

Show Tags

New post 31 Aug 2017, 12:07
MathRevolution wrote:
Machine A can do a job in 24 hours at a constant rate. If Machine A does the job for 8 hours and Machine B does the rest of the job, which works at 2/3 constant rate of Machine A. How long will it take for Machine B alone to do the rest of the job?

A. 12hrs
B. 16hrs
C. 24hrs
D. 28hrs
E. 32hrs


B's time=(3/2)*24=36 hours
(2/3 job)/(1/36 rate)=24 hours
C
Non-Human User
User avatar
Joined: 09 Sep 2013
Posts: 9869
Premium Member
Re: Machine A can do a job in 24 hours at a constant rate and machine A do  [#permalink]

Show Tags

New post 14 Oct 2018, 10:37
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.
_________________

GMAT Books | GMAT Club Tests | Best Prices on GMAT Courses | GMAT Mobile App | Math Resources | Verbal Resources

GMAT Club Bot
Re: Machine A can do a job in 24 hours at a constant rate and machine A do   [#permalink] 14 Oct 2018, 10:37
Display posts from previous: Sort by

Machine A can do a job in 24 hours at a constant rate and machine A do

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


Copyright

GMAT Club MBA Forum Home| About| Terms and Conditions and Privacy Policy| GMAT Club Rules| Contact| Sitemap

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

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.