document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=465894>Question 465894</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A train travels from A to B at 10km per hour and returns from B to A at 15km per hour.  What is the average speed of the train?\r<BR>\n" );
document.write( "\n" );
document.write( "I thought it was 12.5kmph using this:\r<BR>\n" );
document.write( "\n" );
document.write( "10+15=25<BR>\n" );
document.write( "25/2 = 12.5\r<BR>\n" );
document.write( "\n" );
document.write( "The answer is 12kmph, though, and I can't figure out why.  Can anyone help?  Please? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #319278 by </B><A HREF=/tutors/aboutme.mpl?userid=robertb><B>robertb(5830)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=robertb><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=robertb><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=319278\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Take the harmonic mean of the two rates:\r<BR>\n" );
document.write( "\n" );
document.write( "<IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=2%2F%281%2F10+%2B+1%2F15%29+=+12 ALIGN=MIDDLE  ALT=\"2%2F%281%2F10+%2B+1%2F15%29+=+12\"   DISABLED_style= \"max-width:90%; height:auto;\" >kph. </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );