Live GMAT classes with Target Test Prep start Nov 21 and Nov 22. First class free.

See classes
Target Test Prep · GMAT

Choose how you want to prepare

Learn live with an expert or move at your own pace. Every option includes the complete TTP study system.

Newsweek Readers’ Choice Awards 2026 winner: Target Test Prep, #1 Test Prep

Target Test Prep was voted #1 Best Test Prep in the 2026 Newsweek Readers’ Choice™ Awards.

★★★★★5.0563 reviews
GMATLiveTeachStarts Nov 22
Josh Braslow, Target Test Prep GMAT expert
LIVE ONLINE CLASSES

Get Ready for GMAT Test Day Faster with Live Online Classes

with Josh Braslow, 20+ years in test prep

Nov 22 · Josh Braslow
Sun · 9:30 AM to 12:30 PM ET
Included
40 hours of live online classes + 6 months of TTP OnDemand
  • Attend the first class for free
  • Every class is recorded, so you never fall behind
View classes & enroll
Limited seats availableTarget Test Prep
EALiveTeachOnDemandStart anytime
EXECUTIVE ASSESSMENT

Target Test Prep EA OnDemand

Self-paced EA prep. Study on your schedule.

EXECUTIVE ASSESSMENT

with

165+ EA score guarantee
$05-day trial no automatic billing
Schedule
Included
40 hours of live online classes plus six months of access to the complete TTP EA OnDemand course.
  • 165+ EA Score Guarantee
  • 4,100+ Quant, Verbal, and Integrated Reasoning practice questions
  • 400+ hours of in-depth video lessons
  • 3,000+ step-by-step video solutions
View EA class & enroll Start free 5-day trial
Limited cohort · enrollment openTrial includes full course accessTarget Test Prep
GMATOnDemandStart anytime
SELF-PACED MASTERCLASS

Target Test Prep GMAT OnDemand

Complete access from day one. Study on your schedule.

715+ score guarantee
$0to start then $127/mo
  • Personalized study plan and analytics
  • Thousands of lessons and practice questions
Start free 5-day trial
Read 563 reviewsTarget Test Prep

Machine A and machine B process the same work at different

Expert replies
Post new topic Post Reply
Subscribe topic
Previous Topic Next Topic
Legendary Member
Posts: 2604
Joined: Sun Oct 29, 2017 2:04 pmFollowed by: 6 members
by swerve » Thu Apr 26, 2018 8:51 am
Timer
00:00
Your answer
Difficulty–

right wrong

Pick an answer to see how members did

Machine A and machine B process the same work at different rates. Machine C processes work as fast as Machines A & B combined. Machine D processes work three times as fast as Machine C; Machine D’s work rate is also exactly four times Machine B’s rate. Assume all four machines work at fixed unchanging rates. If Machine A works alone on a job, it takes 5 hours and 40 minutes. If all four machines work together on the same job simultaneously, how long will it take all of them to complete it?

A. 8 minutes
B. 17 minutes
C. 35 minutes
D. 1 hour and 15 minutes
E. 1 hours and 35 minutes

The OA is B.

Please, can anyone explain this PS question? I tried to solve it but I can't get the correct answer. Thanks.
Top
Join the discussion
Source: — Problem Solving |

GMAT/MBA Expert

Senior | Next Rank: 100 Posts
Posts: 38
Joined: Mon Mar 19, 2018 6:26 amFollowed by: 1 member

by Keith@ThePrincetonReview » Thu Apr 26, 2018 9:44 am
swerve wrote:Machine A and machine B process the same work at different rates. Machine C processes work as fast as Machines A & B combined. Machine D processes work three times as fast as Machine C; Machine D’s work rate is also exactly four times Machine B’s rate. Assume all four machines work at fixed unchanging rates. If Machine A works alone on a job, it takes 5 hours and 40 minutes. If all four machines work together on the same job simultaneously, how long will it take all of them to complete it?

A. 8 minutes
B. 17 minutes
C. 35 minutes
D. 1 hour and 15 minutes
E. 1 hours and 35 minutes

The OA is B.

Please, can anyone explain this PS question? I tried to solve it but I can't get the correct answer. Thanks.
The information in the question stem can be used to write several equations, relating the rates at which the different machines work.

Machine C works as fast as Machines A and B combined, so C = A + B.
Machine D works three times as fast as Machine C, so D = 3C, and C = (1/3)D.
Machine D works four times as fast as Machine B, so D = 4B, and B = (1/4)D.

Substitute these expressions for B and C into the first equation above, so that (1/3)D = A + (1/4)D.
Rewrite this equation using a common denominator, so that (4/12)D = A + (3/12)D.
Simplify this equation, so that A = (1/12)D.

Machine A works at a rate of 1 job in 5 hours and 40 minutes, or 1 job in 340 minutes. Thus, Machine A works at a rate of 1/340.
Substituting this value into the equation yields the equation 1/340 = (1/12)D.
Simplify, so that D = 12/340, or 12 jobs in 340 minutes.

Then, if B = (1/4)D, it must be the case that B = 3/340. In other words, Machine B works at a rate of 3 jobs every 340 minutes.
And if C = (1/3)D, it must be the case that C = 4/340. In other words, Machine C works at a rate of 4 jobs every 340 minutes.

Add the rates of the 4 machines, so that A + B + C + D = (1/340) + (3/340) + (4/340) + (12/340) = 20/340.
Reduce the fraction, so that all 4 machines working together have a combined rate of 1/17, or 1 job every 17 minutes.

The correct answer is choice B.

Hope this helps.
Top
Join the discussion
User avatar
GMAT Instructor
Posts: 15539
Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members
Location: New York, NY
Thanked: 13060 times
GMAT Score:790

by GMATGuruNY » Thu Apr 26, 2018 10:37 am
swerve wrote:Machine A and machine B process the same work at different rates. Machine C processes work as fast as Machines A & B combined. Machine D processes work three times as fast as Machine C; Machine D’s work rate is also exactly four times Machine B’s rate. Assume all four machines work at fixed unchanging rates. If Machine A works alone on a job, it takes 5 hours and 40 minutes. If all four machines work together on the same job simultaneously, how long will it take all of them to complete it?

A. 8 minutes
B. 17 minutes
C. 35 minutes
D. 1 hour and 15 minutes
E. 1 hours and 35 minutes
Machine D processes work three times as fast as Machine C.
Machine D’s work rate is also exactly four times Machine B’s rate.
Let D = 12 units per minute, implying that C= 4 units per minute and B = 3 units per minute.

Machine C processes work as fast as Machines A and B combined.
Since C = 4 units per minute and B = 3 units per minute, A = 1 unit per minute.

If Machine A works alone on a job, it takes 5 hours and 40 minutes.
Since A working at 1 unit per minute takes 340 minutes to complete the job, we get:
Job = rt = (1)(340) = 340 units.

If all four machines work together on the same job simultaneously, how long will it take all of them to complete it?
Since the combined rate for A+B+C+D = 1+3+4+12 = 20 units per minute, the time for all 4 machines together to complete the 340-unit job = w/r = 340/20 = 17 minutes.

The correct answer is B.
Private tutor exclusively for the GMAT and GRE, with over 20 years of experience.
Followed here and elsewhere by over 1900 test-takers.
I have worked with students based in the US, Australia, Taiwan, China, Tajikistan, Kuwait, Saudi Arabia -- a long list of countries.
My students have been admitted to HBS, CBS, Tuck, Yale, Stern, Fuqua -- a long list of top programs.

As a tutor, I don't simply teach you how I would approach problems.
I unlock the best way for YOU to solve problems.

For more information, please email me (Mitch Hunt) at [email protected].
Student Review #1
Student Review #2
Student Review #3
Top
Join the discussion

GMAT/MBA Expert

User avatar
GMAT Instructor
Posts: 8246
Joined: Sat Apr 25, 2015 10:56 amFollowed by: 29 members
Location: Los Angeles, CA
Thanked: 43 times

hi

by Scott@TargetTestPrep » Fri Apr 27, 2018 9:35 am
swerve wrote:Machine A and machine B process the same work at different rates. Machine C processes work as fast as Machines A & B combined. Machine D processes work three times as fast as Machine C; Machine D’s work rate is also exactly four times Machine B’s rate. Assume all four machines work at fixed unchanging rates. If Machine A works alone on a job, it takes 5 hours and 40 minutes. If all four machines work together on the same job simultaneously, how long will it take all of them to complete it?

A. 8 minutes
B. 17 minutes
C. 35 minutes
D. 1 hour and 15 minutes
E. 1 hours and 35 minutes
Since Machine A’s time to complete the job is 5 hours and 40 minutes, or 5 2/3 = 17/3 hours, its rate is 3/17. We can let Machines B’s rate = b and thus, Machine C’s rate = 3/17 + b and Machine D’s rate = 3(3/17 + b) = 9/17 + 3b. We are also given that Machine D’s rate = 4b. Thus we have:

9/17 + 3b = 4b

9/17 = b

Now, we can determine that C’s rate = 3/17 + 9/17 = 12/17 and D’s rate = 4(9/17) = 36/17.

Thus, if we let x = the time, in hours, for the 4 machines to work together to complete the job, we have:

(3/17)x + (9/17)x + (12/17)x + (36/17)x = 1

[(3 + 9 + 12 + 36)/17]x = 1

(60/17)x = 1

x = 1/(60/17) = 17/60

Thus it takes 17/60 hours, or 17 minutes to complete the job when 4 machines work together.

Answer: B

Scott Woodbury-Stewart
Founder and CEO
[email protected]

Image

See why Target Test Prep is rated 5 out of 5 stars on BEAT the GMAT. Read our reviews

ImageImage
Top
Join the discussion