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# facing problem with these types of questions.

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Intern
Joined: 28 Dec 2009
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facing problem with these types of questions. [#permalink]

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30 Dec 2009, 01:46
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Question Stats:

0% (00:00) correct 100% (00:33) wrong based on 1 sessions

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If ‘A’ can complete a task in 3 hours and ‘B’ can complete the same task in 6 hours, how long will it take if both of them work together to complete the task?

Thanks

Last edited by david01 on 08 Mar 2010, 02:55, edited 1 time in total.

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Manager
Joined: 09 May 2009
Posts: 204

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Re: I am facing problem with these types of questions. [#permalink]

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30 Dec 2009, 03:06
first thing david
the problem never asked about the mean time , the problem is asking how much time it will if bth does the work together . there is a huge diff in bth the cases.

secondly there is a direct formula to handle such problem

if A takes x hrs and B takes y hrs to do a work independently then , combining they will
take x*y/(x+y) hrs

in this case----> 3*6/(3+6)=18/9=2
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Senior Manager
Joined: 22 Dec 2009
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Re: I am facing problem with these types of questions. [#permalink]

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01 Jan 2010, 11:22
The best approach to these problems is to get the 1 hr work done by each participant.

To explain:
If ‘A’ can complete a task in 3 hours and ‘B’ can complete the same task in 6 hours, how long will it take if both of them work together to complete the task?

In 1 hr, A can do $$=\frac{1}{3}$$ Task

Similarly
In 6 hrs, B can do = 1 Task
In 1 hr, B can do $$=\frac{1}{6}$$ Task

Therefore the task done by both A and B in 1 hr $$=\frac{1}{3} + \frac{1}{6} = \frac{1}{2}$$ Task

Now $$\frac{1}{2}$$ Task is done by both A & B in = 1 hr
1 Task (read as complete Task) is done by both A & B in $$= 1 / \frac{1}{2}$$ hrs = 2 hrs

Reason for this detail approach is that with this understanding you can solve questions involving more than 2 people and also with complex combinations....

Hope this helps!

Cheers!
JT
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Re: I am facing problem with these types of questions.   [#permalink] 01 Jan 2010, 11:22
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