Question 993391
.
Thank you for asking.


The first pipe fills {{{1/18}}} of the tank volume in one hour (in each hour).


After  5  hour of working,  this pipe will fill  {{{5/18}}}  of the tank volume,  and  {{{13/18}}}  of the volume will remain still non-filled.


The second pipe fills  {{{1/24}}}  of the tank volume per hour.  When both pipes are at work,  they fill  {{{1/18}}} + {{{1/24}}} = {{{4/72}}} + {{{3/72}}} = {{{7/72}}}  of the tank volume for each hour. 

They will fill the remaining volume of the tank in  {{{13/18}}} : {{{7/72}}}  hours.  Now, 


{{{13/18}}} : {{{7/72}}} = {{{(13*72)/(18*7)}}} = {{{(13*4)/7}}} = {{{52/7}}} = {{{7}}}{{{3/7}}}  hours. 


Hence,  the total time,  measured from the opening of the larger pipe,  to fill the tank is  {{{5}}} + {{{7}}}{{{3/7}}} = {{{12}}}{{{3/7}}}  hour.



Many of typical &nbsp;"joint work"&nbsp; problems are considered and solved in the lesson &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; in this site.


Look in it, &nbsp;and you will improve your skills!


It is free of charge and without registration.