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i falter in rate problems :( though being so easy

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by cans » Wed Jun 01, 2011 10:24 pm
6 machines do work in 12 days
thus it means 1 machine alone can do work in 12*6 = 72 days
to complete work in 8 days, we need 72/8 = 9 machines
Thus additional of 9-6=3 machines.
IMO B
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by Frankenstein » Thu Jun 02, 2011 1:01 am
Hi,
B seems to be correct. Can you check OA again.
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by Ozlemg » Thu Jun 02, 2011 1:09 am
B seems the right answer.

12 days --->6 machines
8 days---> x machines
-------------------------

There is an indirect propotion btw the number of machines and the days.SO,
12*6)/ 8 = 9 machines

9-6 : 3 additional machines are required.
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by divya23 » Thu Jun 02, 2011 1:29 am
ya its 3 sorry ppl
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by galaxian » Thu Jun 02, 2011 9:58 am
A Good way to approach these problems is to Calculate Amount of work done in Man-Days (Machine days)
Like : 9 Man can do in 7 days => 9*7 Man Days of Work
or 6 Machines in 5 Hours => 6*5 Machine Hours of total work has to be done, this makes finding the unknown easier !
divya23 wrote:6 machines,each wrking at same constant rate,together can complete a job in 12 days.How many additional machines,each woeking at the same rate will be needed to comp job in 8 days?
A.2
B.3
C.4
D.6
E.8

[spoiler]OA = C[/spoiler]
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