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

Work rate combination problem

Expert replies
Post new topic Post Reply
Subscribe topic
Previous Topic Next Topic
Junior | Next Rank: 30 Posts
Posts: 14
Joined: Wed Oct 01, 2008 5:59 pm
by sethn23 » Wed Oct 01, 2008 6:15 pm
Each of 10 machines works at a constant rate. When working together the amount of time it takes to complete a job is 16 hrs. How many hours will it take to complete the same job if only 8 machines work together?

18
20
22
24
26
Top
Join the discussion
Source: — Problem Solving |
User avatar
Master | Next Rank: 500 Posts
Posts: 316
Joined: Mon Sep 22, 2008 12:04 amFollowed by: 1 member
Thanked: 36 times

Re: Work rate combination problem

by Morgoth » Wed Oct 01, 2008 6:34 pm
sethn23 wrote:Each of 10 machines works at a constant rate. When working together the amount of time it takes to complete a job is 16 hrs. How many hours will it take to complete the same job if only 8 machines work together?

18
20
22
24
26
rate * time * no. of machines = work

rate * 16 * 10 = 1

rate = 1/160

rate * time * no. of machines = work

1/160*time*8= 1

time = 160/8 = 20.

Hope this helps.
Top
Join the discussion
Junior | Next Rank: 30 Posts
Posts: 14
Joined: Wed Oct 01, 2008 5:59 pm

by sethn23 » Wed Oct 01, 2008 6:38 pm
thanks again Morgoth
Top
Join the discussion
Newbie | Next Rank: 10 Posts
Posts: 9
Joined: Tue Jun 10, 2008 11:34 am

by allechat » Thu Oct 02, 2008 12:38 pm
could you also look at this as, # of machines is reduced by 1/5, so it's going to take 1/5 more time?

20 is 1/5 more time than 16.

change formula: (10-8)/10 machines= 1/5 fewer machines

then (x-16)/x=1/5, 5x-80=x
5x=x+80, x=20
Top
Join the discussion
Junior | Next Rank: 30 Posts
Posts: 25
Joined: Fri Jan 23, 2009 11:57 am
Location: Minneapolis
Thanked: 1 times

Very simple formula

by peddisetty » Sun Feb 15, 2009 3:39 pm
You can use M1D1W2 = M2D2W1.

So, here its M1D1 = M2D2 => 10*16 = 8*x

x = 20.

Very simple........
Raj Peddisetty
Top
Join the discussion
User avatar
Master | Next Rank: 500 Posts
Posts: 319
Joined: Wed Feb 04, 2009 10:32 amFollowed by: 9 members
Location: Delhi
Thanked: 84 times

by sureshbala » Tue Feb 17, 2009 7:59 pm
Since 10 machines take 16 hrs, it is clear that the work takes 160 machine hours. Since now we have 8 machines, to contribute those 160 machine hours, time taken is 160/8 = 20.

The same thing is explained above in the form of a forumula
Top
Join the discussion
Junior | Next Rank: 30 Posts
Posts: 27
Joined: Sat Feb 07, 2009 6:14 pmFollowed by: 1 member
Location: Las Vegas, NV
Thanked: 7 times
GMAT Score:760

Re: Work rate combination problem

by griscomtestprep » Wed Feb 18, 2009 12:23 am
sethn23 wrote:Each of 10 machines works at a constant rate. When working together the amount of time it takes to complete a job is 16 hrs. How many hours will it take to complete the same job if only 8 machines work together?

18
20
22
24
26
Since there are 8/10 of the machines, it is going to take 10/8 as long.
10/8 * 16 = 20
Free Hour of Live Online GMAT Training
Griscom Test Prep
www.griscomtestprep.net
[email protected]
702-406-7688
Top
Join the discussion
Master | Next Rank: 500 Posts
Posts: 117
Joined: Wed Jun 09, 2010 7:02 am

by missrochelle » Wed Aug 25, 2010 9:07 pm
sethn23 wrote:Each of 10 machines works at a constant rate. When working together the amount of time it takes to complete a job is 16 hrs. How many hours will it take to complete the same job if only 8 machines work together?

18
20
22
24
26
What are you supposed to recognize in this problem that states the total time is 160hrs? I assumed each machine worked 1/16 hr which is wrong...
Top
Join the discussion