Question 354083
first pipe = 6 hours
so it can do 1/6 of the job in 1 hour.
so in 2 hours it has done 1/3 of the of the job.
Balance job remaining = 1-1/3 = 2/3 of the job.
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Time taken by three pipes to complete balance job
pipe 1- 4 hours
pipe 2- 8/3 hours
pipe 3 = 14/3 hours

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1/4+3/8 -3/14 of the job they will do in 1 hour

0.41 of the job they do in1 hour.
1/0.41 hours they will take to do 2/3 of the job
=2.4 hours 
+ 2hours (pipe one alone)
= 4.4 hours
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m.ananth@hotmail.ca