Pipes and Cisterns.....[competitive. exam prep.... topic 3]


Pipes and Cisterns problems are almost the same as those of Time and Work problems. Thus, if a pipe fills a
tank in 6 hrs, then the pipe fills
1/6th of the tank in 1 hour. The only difference with Pipes and Cisterns
problems is that there are outlets as well as inlets. Thus, there are agents (the outlets) which perform negative
work too. The rest of the process is almost similar.
Inlet:A pipe connected with a tank (or a cistern or a reservoir) is called an inlet, if it fills the tank. The work
done by this is taken as positive work.
Outlet:A pipe connected with a tank is called an, outlet, if it empties the tank and the work done by this is
taken as the negative work.
Question:-Four men can do work in 15 days. If a man left the work after 5 days and again joined after 5 more days, The remaining three work continuously till the end of work. How many more days
than the estimated, it takes to complete the work?
Sol. After 15 days, the work that is left is equal to the amount of work, that can be done by 1 man in 5 days.
This work can be done in 5/4 days by the 4 men. So it takes 5/4 more days to complete the work

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