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meera
 Post subject: Rate of work done problem
PostPosted: Thu May 25, 2006 8:43 am 
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Learning the ABCs

Joined: Thu May 25, 2006 8:34 am
Posts: 7
I have been facing problems with questions of this kind

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 the two of them work together to complete the task?

I thought it took (3 + 6) / 2 = 4.5 Mean of the time taken by the two. Anyways, my answer is wrong.

Please explain the logic. :?:
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crack1600
 Post subject:
PostPosted: Thu May 25, 2006 8:50 am 
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Learning the ABCs

Joined: Thu May 25, 2006 8:47 am
Posts: 4
This is not a average or arithmetic mean question.

If A can complete the task in 3 hours, he would complete 1/3rd of the task in an hour.

B will complete 1/6th of the task in an hour.

So working together, in an hour they will complete 1/3 + 1/6 of the task.

or 3/6th of the task. The work will be over in 2 hours.
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nandu
 Post subject: Re: Rate of work done problem
PostPosted: Fri May 26, 2006 12:01 pm 
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Learning the ABCs

Joined: Thu May 25, 2006 8:46 am
Posts: 9
meera wrote:
I thought it took (3 + 6) / 2 = 4.5 Mean of the time taken by the two. Anyways, my answer is wrong.



If A alone can complete the task in 3 hours, then with some help A should take less than 3 hours. So, that is clue that it will not be an Arithmetic mean 8)
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