document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=928955>Question 928955</A>: <I><SPAN STYLE=\"word-break: break-all;\"> A hydrofoil made a round-trip of 144 km in 4 hours. because of headwinds the average speed on returning was 15 km/h less than the average speed going out.  find both individual speeds (going out and returning) </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #564005 by </B><A HREF=/tutors/aboutme.mpl?userid=TimothyLamb><B>TimothyLamb(4379)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=TimothyLamb><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=TimothyLamb><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=564005\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> x = speed outbound<BR>\n" );
document.write( "speed inbound = x - 15<BR>\n" );
document.write( "---<BR>\n" );
document.write( "y = time outbound<BR>\n" );
document.write( "z = time inbound<BR>\n" );
document.write( "---<BR>\n" );
document.write( "w = distance of one leg (outbound or inbound) = 144/2 = 72 km<BR>\n" );
document.write( "---<BR>\n" );
document.write( "s = d/t<BR>\n" );
document.write( "---<BR>\n" );
document.write( "outbound:<BR>\n" );
document.write( "x = w/y<BR>\n" );
document.write( "x = 72/y<BR>\n" );
document.write( "y = 72/x<BR>\n" );
document.write( "---<BR>\n" );
document.write( "inbound:<BR>\n" );
document.write( "x - 15 = w/z<BR>\n" );
document.write( "x - 15 = 72/z<BR>\n" );
document.write( "---<BR>\n" );
document.write( "total time:<BR>\n" );
document.write( "y + z = 4<BR>\n" );
document.write( "---<BR>\n" );
document.write( "y + z = 4<BR>\n" );
document.write( "y = 72/x<BR>\n" );
document.write( "72/x + z = 4<BR>\n" );
document.write( "---<BR>\n" );
document.write( "72/x + z = 4<BR>\n" );
document.write( "z = 4 - 72/x<BR>\n" );
document.write( "---<BR>\n" );
document.write( "x - 15 = 72/z<BR>\n" );
document.write( "z(x - 15) = 72<BR>\n" );
document.write( "z = 4 - 72/x<BR>\n" );
document.write( "(4 - 72/x)(x - 15) = 72<BR>\n" );
document.write( "4x - 60 - 72 + 1080/x = 72<BR>\n" );
document.write( "x(4x - 132 + 1080/x = 72)<BR>\n" );
document.write( "4xx - 132x + 1080 = 72x<BR>\n" );
document.write( "4xx - 204x + 1080 = 0<BR>\n" );
document.write( "---<BR>\n" );
document.write( "the above quadratic equation is in standard form, with a=4, b=-204 and c=1080<BR>\n" );
document.write( "---<BR>\n" );
document.write( "to solve the quadratic equation, by using the quadratic formula, copy and paste this:<BR>\n" );
document.write( "4 -204 1080<BR>\n" );
document.write( "into this solver: https://sooeet.com/math/quadratic-equation-solver.php<BR>\n" );
document.write( "---<BR>\n" );
document.write( "the quadratic has two real roots at:<BR>\n" );
document.write( "---<BR>\n" );
document.write( "x = 45<BR>\n" );
document.write( "x = 6<BR>\n" );
document.write( "---<BR>\n" );
document.write( "the root x=6 doesn't fit the problem statement, as it forces the speed inbound (x-15) to be negative, so use the root x=45:<BR>\n" );
document.write( "---<BR>\n" );
document.write( "answer:<BR>\n" );
document.write( "x = speed outbound = 45 kph<BR>\n" );
document.write( "speed inbound = x-15 = 30 kph<BR>\n" );
document.write( "---<BR>\n" );
document.write( "Solve and graph linear equations:<BR>\n" );
document.write( "https://sooeet.com/math/linear-equation-solver.php<BR>\n" );
document.write( "---<BR>\n" );
document.write( "Solve quadratic equations, quadratic formula:<BR>\n" );
document.write( "https://sooeet.com/math/quadratic-formula-solver.php<BR>\n" );
document.write( "---<BR>\n" );
document.write( "Solve systems of linear equations up to 6-equations 6-variables:<BR>\n" );
document.write( "https://sooeet.com/math/system-of-linear-equations-solver.php </SPAN>\n" );
document.write( "</TD></TR></TABLE>\n" );