Question 1191719
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12. An aquarium can be filled by two inlets in 0.4 h and 0.25 h,
respectively, and emptied by an outlet in 0.5 h. How long would it
take to fill the aquarium if the inlets and outlet were operating
simultaneously?
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<pre>
First  inlet filling rate is  {{{1/0.4}}} = 2.5 volumes per hour.


Second inlet filling rate is  {{{1/0.25}}} = 4 volumes per hour.


The total filling rate is  2.5 + 4 = 6.5 volumes per hour.


The draining rate is  {{{1/0.5}}} = 2 volumes per hour.


The net filling rate (accounting for draining, too) is  6.5 - 2 = 4.5 volumes per hour.


The time for filling with all inlets and the outlet operating is  

    {{{1/4.5}}} of an hour = {{{2/9}}}  of an hour = {{{(2*60)/9}}} minutes = {{{40/3}}} minutes = 13 minutes and 20 seconds.    <U>ANSWER</U>
</pre>

Solved.