NEW HERE? LEARN MORE
closeclose
Last visit was: 27 Apr 2024, 16:33 It is currently 27 Apr 2024, 16:33
Decision Tracker
My Rewards
New posts
New comers' posts

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.
Go to My Error Log Learn more
Close
Request Expert Reply
Confirm Cancel

Work and rate problem

SORT BY:
Date
Kudos
Tags:
Find Similar Topics 
Show Tags
Hide Tags
avatar
G
Shiv2016
Director
Director
Joined: 02 Sep 2016
Posts: 528
Own Kudos [?]: 194 [0]
Given Kudos: 275
Work and rate problem [#permalink] New post   15 Aug 2017, 23:30
Hello BrushMyQuant, abhimahna, and Bunuel

If we are given that A can do a work in 12 hours and B can do the same work in 18 hours. A started the work and B joined him after 6 hours. How much time will they both take to complete the work?


Let total work = 36
A can do 3 units per hour
B can do 2 units per hour

Together they finish 5 units per hour


A started the work and worked alone for 6 hours. Therefore A finished 18 units of work.

Amount of work left= 36-18= 18

I am confused about the steps from here.

What I dis was, I found new units per hour for both A and B

A= 3/2 UNITS/HOUR
B= 1 UNIT/HOUR

AND got the answer 36/5 which is incorrect.

What is the error in the above method?
User avatar
L
abhimahna
Board of Directors
Joined: 18 Jul 2015
Status:Emory Goizueta Alum
Posts: 3600
Own Kudos [?]: 5429 [0]
Given Kudos: 346
Send PM
Reviews Badge
Work and rate problem [#permalink] New post   15 Aug 2017, 23:42
Expert Reply
Shiv2016 wrote:
I am confused about the steps from here.

What I dis was, I found new units per hour for both A and B

A= 3/2 UNITS/HOUR
B= 1 UNIT/HOUR

AND got the answer 36/5 which is incorrect.

What is the error in the above method?


Hi Shiv2016 ,

The steps highlighted above are incorrect.

Why are you calculating the new unit of work? I mean you cannot say that the efficiency of A and B would change when the work left is less.

As per your method, you found that both A and B are doing the work at 5 units/hour.

Work left when B joined = 18 units.

If they are doing at the rate of 5 units per hour, total time taken to complete the whole work = 18/5 = 3 hours and 36 mins.

Does that make sense?
avatar
G
Shiv2016
Director
Director
Joined: 02 Sep 2016
Posts: 528
Own Kudos [?]: 194 [0]
Given Kudos: 275
Re: Work and rate problem [#permalink] New post   16 Aug 2017, 00:03
abhimahna wrote:
Shiv2016 wrote:
I am confused about the steps from here.

What I dis was, I found new units per hour for both A and B

A= 3/2 UNITS/HOUR
B= 1 UNIT/HOUR

AND got the answer 36/5 which is incorrect.

What is the error in the above method?


Hi Shiv2016 ,

The steps highlighted above are incorrect.

Why are you calculating the new unit of work? I mean you cannot say that the efficiency of A and B would change when the work left is less.

As per your method, you found that both A and B are doing the work at 5 units/hour.

Work left when B joined = 18 units.

If they are doing at the rate of 5 units per hour, total time taken to complete the whole work = 18/5 = 3 hours and 36 mins.

Does that make sense?



abhimahna thank you for your reply.

When we find their efficiency for completing the work, we find it according to the amount of work given. Won't it change when the amount of work will change?
User avatar
L
abhimahna
Board of Directors
Joined: 18 Jul 2015
Status:Emory Goizueta Alum
Posts: 3600
Own Kudos [?]: 5429 [0]
Given Kudos: 346
Send PM
Reviews Badge
Re: Work and rate problem [#permalink] New post   16 Aug 2017, 00:12
Expert Reply
Shiv2016 wrote:
abhimahna thank you for your reply.

When we find their efficiency for completing the work, we find it according to the amount of work given. Won't it change when the amount of work will change?


Hi Shiv2016 ,

Again the highlighted line is incorrect.

When we are given A can complete a work in 12 hours, his efficiency will remain the same no matter how much work is left unless you are told that A is changing his efficiency.

Since A and B have combined efficiency of 5 units/hour, it will remain the same and we will find the time accordingly.

Does that make sense?
GMAT Club Bot
gmatclubot
Re: Work and rate problem [#permalink]
16 Aug 2017, 00:12
Moderator:
Bunuel
Math Expert
92959 posts

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne
Main navigation
GMAT Resources
Partners
MBA Resources
www.gmac.com|www.mba.com | | GMAT Club Rules | Terms and Conditions