document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=252822>Question 252822</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Flying east between two cities, a plane's speed is 380 mph.  On the return trip it flies at 420 mph.  Find the average speed over the whole round trip.  (NO, the answer is not 400 mph.) </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #184921 by </B><A HREF=/tutors/aboutme.mpl?userid=Alan3354><B>Alan3354(69443)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=Alan3354><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=Alan3354><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=184921\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Here's a similar problem I did yesterday.\r<BR>\n" );
document.write( "\n" );
document.write( "If you need further help, or to check your work, email via the thank you note.<BR>\n" );
document.write( "==================================================================<BR>\n" );
document.write( "A cyclist bikes x distance at 10 miles per hour and returns over the same path at 8 miles per hour. What is the cyclist's average rate for the round trip in miles per hour?<BR>\n" );
document.write( "---------------------<BR>\n" );
document.write( "d= rt --> t = d/r<BR>\n" );
document.write( "t = x/10 + x/8 = 9x/40<BR>\n" );
document.write( "r = 2d/t = 2x/t --- 2x for the round trip<BR>\n" );
document.write( "r = (2x/1)/(9x/40) = 80x/9x<BR>\n" );
document.write( "r = 80/9 = 8.888... mph<BR>\n" );
document.write( "---------------------------<BR>\n" );
document.write( "It's not the average, 9 mph, because he spent more time going 8 mph than he did going 10 mph.<BR>\n" );
document.write( "---------------<BR>\n" );
document.write( "That's the basis of the famous Michelson-Morley experiment that disproved the existence of the \"ether\" is space. </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );