It is currently 15 Dec 2017, 08:17

Decision(s) Day!:

CHAT Rooms | Olin (St. Louis) R1 | Tuck R1 | Ross R1 | Fuqua R1


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

Events & Promotions in June
Open Detailed Calendar

Machine A can do a certain job in 8 hours. Machine B can do the same

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

Hide Tags

Expert Post
Math Expert
User avatar
V
Joined: 02 Sep 2009
Posts: 42615

Kudos [?]: 135739 [0], given: 12707

Machine A can do a certain job in 8 hours. Machine B can do the same [#permalink]

Show Tags

New post 07 Feb 2016, 09:12
Expert's post
1
This post was
BOOKMARKED
00:00
A
B
C
D
E

Difficulty:

  85% (hard)

Question Stats:

61% (02:00) correct 39% (02:00) wrong based on 138 sessions

HideShow timer Statistics

Machine A can do a certain job in 8 hours. Machine B can do the same job in 10 hours. Machine C can do the same job in 12 hours. All three machines start the job at 9:00 a.m. Machine A breaks down at 11:00 a.m., and the other two machines finish the job. Approximately what time will the job be finished?

A. Noon
B. 12:30 p.m.
C. 1:00 p.m.
D. 1:30 p.m.
E. 2:00 p.m.
[Reveal] Spoiler: OA

_________________

New to the Math Forum?
Please read this: Ultimate GMAT Quantitative Megathread | All You Need for Quant | PLEASE READ AND FOLLOW: 12 Rules for Posting!!!

Resources:
GMAT Math Book | Triangles | Polygons | Coordinate Geometry | Factorials | Circles | Number Theory | Remainders; 8. Overlapping Sets | PDF of Math Book; 10. Remainders | GMAT Prep Software Analysis | SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) | Tricky questions from previous years.

Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


What are GMAT Club Tests?
Extra-hard Quant Tests with Brilliant Analytics

Kudos [?]: 135739 [0], given: 12707

1 KUDOS received
Intern
Intern
avatar
Joined: 26 Feb 2015
Posts: 5

Kudos [?]: 2 [1], given: 0

Re: Machine A can do a certain job in 8 hours. Machine B can do the same [#permalink]

Show Tags

New post 08 Feb 2016, 19:21
1
This post received
KUDOS
Ans: C (1:00pm)

From 9:00-11:00c(2 hrs)

A can do 1/8 Job/hr. so in 2 hours he can do 1/4 job.
B can do 1/10 job/hr so in 2 hrs. he can do 1/5 Job.
C can do 1/12 job/hr so in 2 hours he can do 1/6 job.

Total = 1/4+1/5+1/6 = 37/60 Job

Now balance work needs to be done by B and C.
Balance Work= 23/60 Job

Combined rate of B and C = 1/10+1/12 = 11/60 job/hr.
So they will do 22/60 work in 2 hrs (approx. to the balance work of 23/60)

Hence the Job will be completed 2hrs. after 11:00 i.e. @ 1:00pm

Ans: C (1:00pm)

Kudos [?]: 2 [1], given: 0

Intern
Intern
avatar
Joined: 14 Dec 2014
Posts: 19

Kudos [?]: 7 [0], given: 30

Concentration: Technology
GMAT ToolKit User
Re: Machine A can do a certain job in 8 hours. Machine B can do the same [#permalink]

Show Tags

New post 13 Feb 2016, 11:52
Bunuel wrote:
Machine A can do a certain job in 8 hours. Machine B can do the same job in 10 hours. Machine C can do the same job in 12 hours. All three machines start the job at 9:00 a.m. Machine A breaks down at 11:00 a.m., and the other two machines finish the job. Approximately what time will the job be finished?

A. Noon
B. 12:30 p.m.
C. 1:00 p.m.
D. 1:30 p.m.
E. 2:00 p.m.


The numbers in this problem make it a little challenging, so it takes a bit longer to do the regular rate = work / time method:

Combined rate of machines A,B,C: (15+12+10) / 120 = 37 /120
Time for all three machines = 2 hrs
Work completed= (37/120) * 2 = 74 / 120 :?

Work left: 120 - 74 = 46 /120 :|

Combined rate of machines B and C: ( 6 + 5) / 60 = 11/60
Time to complete remaining work: (46/120) / (11/60) = 46/120 * 60/11 = 23/11 =~ 2hrs

Kudos [?]: 7 [0], given: 30

Expert Post
Target Test Prep Representative
User avatar
S
Status: Head GMAT Instructor
Affiliations: Target Test Prep
Joined: 04 Mar 2011
Posts: 1810

Kudos [?]: 981 [0], given: 5

Re: Machine A can do a certain job in 8 hours. Machine B can do the same [#permalink]

Show Tags

New post 27 Nov 2017, 11:35
Expert's post
1
This post was
BOOKMARKED
Bunuel wrote:
Machine A can do a certain job in 8 hours. Machine B can do the same job in 10 hours. Machine C can do the same job in 12 hours. All three machines start the job at 9:00 a.m. Machine A breaks down at 11:00 a.m., and the other two machines finish the job. Approximately what time will the job be finished?

A. Noon
B. 12:30 p.m.
C. 1:00 p.m.
D. 1:30 p.m.
E. 2:00 p.m.


We can let the rate of machines A, B, and C be 1/8, 1/10, and 1/12, respectively.

When they all work for two hours they complete the following portion of the job:

(1/8) x 2 + (1/10) x 2 + (1/12) x 2 = 1/4 + 1/5 + 1/6

15/60 + 12/60 + 10/60 = 37/60

So 23/60 is left to be done after 11:00 am.

The combined rate of machines B and C is 1/10 + 1/12 = 6/60 + 5/60 = 11/60.

Thus, the time for machines B and C to finish the job is:

(23/60)/(11/60) = 23/60 x 60/11 = 23/11 = 2 1/11 ≈ 2 hours

Thus, the job was completed at about 11:00 am + 2 hours = 1:00 pm.

Answer: C
_________________

Jeffery Miller
Head of GMAT Instruction

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

Kudos [?]: 981 [0], given: 5

Re: Machine A can do a certain job in 8 hours. Machine B can do the same   [#permalink] 27 Nov 2017, 11:35
Display posts from previous: Sort by

Machine A can do a certain job in 8 hours. Machine B can do the same

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


GMAT Club MBA Forum Home| About| Terms and Conditions| 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®.