document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1205975>Question 1205975</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Josh can clean the math building on his campus in 3 hours. Ken takes 7 hours to clean the same building. If they work​ together, how long will it take them to clean this​ building?\r<BR>\n" );
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document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #843099 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=843099\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> <br><BR>\n" );
document.write( "(1) The classic algebraic solution method (but presented informally)....<br><BR>\n" );
document.write( "John cleans 1/3 of the building in 1 hour<BR>\n" );
document.write( "Ken cleans 1/7 of the building in 1 hour<BR>\n" );
document.write( "Together the fraction of the building they clean in 1 hour is 1/3+1/7 = 7/21+3/21 = 10/21<BR>\n" );
document.write( "So the number of hours it takes them to clean the building together is 21/10 hours.<br><BR>\n" );
document.write( "(2) An alternative method, also presented informally....<br><BR>\n" );
document.write( "Consider the least common multiple of the two times, which is 3*7 = 21 hours<BR>\n" );
document.write( "In 21 hours, John could clean the building 21/3 = 7 times<BR>\n" );
document.write( "In 21 hours, Ken could clean the building 21/7 = 3 times<BR>\n" );
document.write( "So in 21 hours the two of them could clean the building 7+3 = 10 times<BR>\n" );
document.write( "So the time it takes them to clean the building once is 21/10 hours.<br><BR>\n" );
document.write( "(3) The standard shortcut....<br><BR>\n" );
document.write( "If the two workers individually can do the job in A hours and B hours, then the number of hours it takes them to do the job together is (AB)/(A+B).  In this problem, (7*3)/(7+3) = 21/10.<br><BR>\n" );
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