Question 1032971
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A water tank can be filled in 20 hours by an inlet pipe and emptied in 25 hours by an outlet pipe. How long will it take to fill the tank if both pipes are left open? 
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Each hour, 1/20 of the tank flows in and 1/25 of the tank flows out.


So, the net balance is {{{1/20 - 1/25}}} = {{{25/500 - 20/500}}} = {{{5/500}}} = {{{1/100}}} of the tank volume is filling each hour.


Therefore, it will take 100 hour to fill the tank if both pipes are left open.


<U>Answer</U>. 100 hours.



You can find many other similar solved joint-work problems in the lessons

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=http://www.algebra.com/algebra/homework/Rate-of-work-word-problems/Word-problems-WORKING-TOGETHER-by-Fractions.lesson>Using Fractions to solve word problems on joint work</A>,

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=http://www.algebra.com/algebra/homework/Rate-of-work-word-problems/Solving-more-complicated-word-problems-on-joint-work.lesson>Solving more complicated word problems on joint work</A>,

&nbsp;&nbsp;&nbsp;&nbsp;- <A HREF=https://www.algebra.com/algebra/homework/Rate-of-work-word-problems/Selected-problems-from-the-archive-on-joint-work-word-problems.lesson>Selected joint-work word problems from the archive</A> 

in this site.


It is good material for you to learn it and to get trained in solution of joint-work problems.