document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1200985>Question 1200985</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A water tank can be filled by an inlet pipe in  <BR>\n" );
document.write( "9<BR>\n" );
document.write( "  hours. It takes  <BR>\n" );
document.write( "4<BR>\n" );
document.write( "  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? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #835213 by </B><A HREF=/tutors/aboutme.mpl?userid=greenestamps><B>greenestamps(13200)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=greenestamps><IMG SRC=http://www.algebra.com/images/aboutme-small.gif BORDER=0 alt=\"About Me\" VALIGN=MIDDLE></A>&nbsp;<IMG SRC=http://www.algebra.com/cgi-bin/show-face.mpl?user=greenestamps><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=835213\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> <br><BR>\n" );
document.write( "Here are a couple of quick informal methods for solving the problem, if a formal algebraic solution, as shown by the other tutors, is not required.<br><BR>\n" );
document.write( "It takes the inlet pipe 9 hours to fill the pool, so it takes 4*9 = 36 hours for the drain pipe to empty it.<br><BR>\n" );
document.write( "Consider a time length of 36 hours -- the least common multiple of 9 hours and 36 hours.  In 36 hours the inlet pipe could fill the pool 4 times, while in 36 hours the drain pipe could empty it once.  So in 36 hours with the inlet pipe and drain pipe both open, they could fill the pool 4-1 = 3 times.<br><BR>\n" );
document.write( "But that means the two together could fill the one pool in 36/3 = 12 hours.<br><BR>\n" );
document.write( "And here is another quick path to the solution, using logical reasoning.<br><BR>\n" );
document.write( "Since the drain pipe works 1/4 as fast as the inlet pipe, when both pipes are working the pool gets filled only 3/4 as fast as when the drain pipe is closed.  And since it normally takes the inlet pipe 9 hours to fill the tank, the amount of time it takes the pool to fill when the drain pipe is open is 9/(3/4) = 9*(4/3) = 12 hours.<br><BR>\n" );
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