SOLUTION: Q1. two pipes can fill a tank in 20 & 15 mins repectively. A third can empty a tank in 10 mins. If the tank is empty & all 3 pipes are opened together, how much time will it take t

Algebra ->  Rate-of-work-word-problems -> SOLUTION: Q1. two pipes can fill a tank in 20 & 15 mins repectively. A third can empty a tank in 10 mins. If the tank is empty & all 3 pipes are opened together, how much time will it take t      Log On


   

Question 325337: Q1. two pipes can fill a tank in 20 & 15 mins repectively. A third can empty a tank in 10 mins. If the tank is empty & all 3 pipes are opened together, how much time will it take to fill the tank completely in mis??
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
one pipe can fill in 20 min
it can do 1/20 of the job in 1minute
the other in 15 mins
this can do 1/15 of the job in 1 minute
..
together they can do 1/15 + 1/20 of the job in 1 minute
=4+3 /60 = 7/60 of the job.
..
the draining is done in 10 minutes
it can do 1/10 of the job in 1 minute.
..
when all three are open the effective filling will be
7/60 -1/10
=7-6/60
=1/60 of the job in 1 minute
so the tank wil be filled in 60 minutes.