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Director
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A qualified worker digs a well in 5 hours. He invites 2 [#permalink]
 14 Jun 2007, 10:34
A qualified worker digs a well in 5 hours. He invites 2 apprentices who work 3/4 as fast and
2 trainees who work 1/5 as fast as he does. If the five-person team digs the same well, how much time
does the team need to finish the job?
a.1.20
b.1.30
c.1.40
d.1.50
e.2.10
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GMAT the final frontie!!!.
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Director
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My choice is B: 1.30 approx...
What is the OA?
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Manager
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Q rate/day = 1/5
A=(3/4)(1/5)=(3/20)(2)=3/10
T=(1/5)(1/5)=(1/25)(2)=2/25
t(1/5+3/10+2/25)=1 = 29/50 --> t= 50/29 or 1:40
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Manager
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Right, it is C! made a mistake
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CEO
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Well done XY, I solved it exactly the same way. Tip for people looking for quicker ways / short cuts, as soon as you reach 50/29, if 50/29 is NOT one of the choices, approximate !!!
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Director
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bsd_lover wrote: Well done XY, I solved it exactly the same way. Tip for people looking for quicker ways / short cuts, as soon as you reach 50/29, if 50/29 is NOT one of the choices, approximate !!!
50/29 is appx 1.7...so..D.. 
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Manager
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Juaz, you'd be right if the hour had 100 minutes.
Since we know that it has 60 mins, 50/29 times 60 gives us a little over 100 min. 100 min is an hour and 40!
Ans is C!
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Manager
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I must be totally blind! I do not see how you can get 1.4 hours out of 50/29.
Here's how I see it: each hour 29/50 of the job is completed, therefore after the first hour, 29/50 is complete and 21/50 is still remaining to be completed. 21/50 is just slightly less than 29/50, which is inline with the 1.7 that Juaz got.
Can someone please explain what I am missing? 
Thanks!
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Manager
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Bluebird wrote: I must be totally blind! I do not see how you can get 1.4 hours out of 50/29. Here's how I see it: each hour 29/50 of the job is completed, therefore after the first hour, 29/50 is complete and 21/50 is still remaining to be completed. 21/50 is just slightly less than 29/50, which is inline with the 1.7 that Juaz got. Can someone please explain what I am missing? Thanks! 50/29 = 1.7 hrs
(.7)60 = approx 40 mins
so total time = 1 hour and 40 mins.
I think the answers are a bit confusing.
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Manager
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Thank you salr15! I am quite embarrassed, but you're right, the answers are a bit confusing... 1.4 to me means 1.4 hours, not 1 hr and 40 minutes. Thank you for the clarification!
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Intern
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Well, technically --- the question asks:
"how much time does the team need to finish the job?"
After the work calculation, we are left with 50/29 hours. This is equivalent to 1 hour and 21/29*60 minutes.
21/29 roughly yields "0.7241" which multiplied by 60 is roughly equivalent to 43.4 minutes.
Therefore, if we give the team 1:40 minutes, they will NOT be able to complete the job. --- Amongst the available choices, the team NEEDS 1:50 minutes to complete the job.
Is my logic wrong on this?
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Intern
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Well, technically --- the question asks:
"how much time does the team need to finish the job?"
After the work calculation, we are left with 50/29 hours. This is equivalent to 1 hour and 21/29*60 minutes.
21/29 roughly yields "0.7241" which multiplied by 60 is roughly equivalent to 43.4 minutes.
Therefore, if we give the team 1:40 minutes, they will NOT be able to complete the job. --- Amongst the available choices, the team NEEDS 1:50 minutes to complete the job.
Is my logic wrong on this?
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