<PRE><B>Question 1200985</B>
.
A water tank can be filled by an inlet pipe in 9 hours. 
It takes 4 times as long for the outlet pipe to empty the tank. 
How long will it take to fill the tank if both pipes are open?
~~~~~~~~~~~~~~~~~~



&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;The &quot;solution&quot; by @josgarithmetic, giving the answer &amp;nbsp;{{{36/5}}} &amp;nbsp;hours, &amp;nbsp;is incorrect and absurdist.

&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;I came to bring a correct solution.



&lt;pre&gt;
The rate of filling is  {{{1/9}}}  of the tank volume per hour.


The rate of draining is  {{{1/36}}}  of the tank volume per hour.


The net rate of filling is the difference  

    {{{1/9 - 1/36}}} = {{{4/36-1/36}}} = {{{3/36}}} = {{{1/12}}}  of the tank volume per hour.


It means that under given conditions, the tank will be filled in 12 hours.    &lt;U&gt;ANSWER&lt;/U&gt;
&lt;/pre&gt;

Solved.


------------------


It is a standard and typical joint work problem.


There is a wide variety of similar solved joint-work problems with detailed explanations in this site. &amp;nbsp;See the lessons

&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;- &lt;A HREF=http://www.algebra.com/algebra/homework/Rate-of-work-word-problems/Word-problems-WORKING-TOGETHER-by-Fractions.lesson&gt;Using Fractions to solve word problems on joint work&lt;/A&gt; 

&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;- &lt;A HREF=http://www.algebra.com/algebra/homework/Rate-of-work-word-problems/Solving-more-complicated-word-problems-on-joint-work.lesson&gt;Solving more complicated word problems on joint work&lt;/A&gt; 

&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;- &lt;A HREF=https://www.algebra.com/algebra/homework/Rate-of-work-word-problems/Selected-problems-from-the-archive-on-joint-work-word-problems.lesson&gt;Selected joint-work word problems from the archive&lt;/A&gt; 



Read them and get be trained in solving joint-work problems.


Also, &amp;nbsp;you have this free of charge online textbook in ALGEBRA-I in this site

&amp;nbsp;&amp;nbsp;&amp;nbsp;&amp;nbsp;- &lt;A HREF=https://www.algebra.com/algebra/homework/quadratic/lessons/ALGEBRA-I-YOUR-ONLINE-TEXTBOOK.lesson&gt;ALGEBRA-I - YOUR ONLINE TEXTBOOK&lt;/A&gt;.


The referred lessons are the part of this textbook under the topic 
&quot;&lt;U&gt;Rate of work and joint work problems&lt;/U&gt;&quot; &amp;nbsp;of the section &amp;nbsp;&quot;&lt;U&gt;Word problems&lt;/U&gt;&quot;.



Save the link to this online textbook together with its description


Free of charge online textbook in ALGEBRA-I
https://www.algebra.com/algebra/homework/quadratic/lessons/ALGEBRA-I-YOUR-ONLINE-TEXTBOOK.lesson


to your archive and use it when it is needed.



</PRE>