document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=243046>Question 243046</A>: <I><SPAN STYLE=\"word-break: break-all;\"> 2 trains, A and B travelling at a constant speeds left 2 different stations 640km apart. Train A started at noon and train B at 1pm. Travelling on parallel tracks towards each other, they passed each other at 4pm. If train A travelled at a speed of x km/h and train B was 20km/h slower than train A,\r<BR>\n" );
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document.write( "(i) write an expression, in terms of x, for the speed of Train B\r<BR>\n" );
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document.write( "(ii)write an expression, in terms of x, for the distance covered by train A just before it passed train B </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #178060 by </B><A HREF=/tutors/aboutme.mpl?userid=oberobic><B>oberobic(2304)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=oberobic><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/images/nopicture.jpg><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=178060\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Fundamentally, this is a distance equation, so w start with D = RT as our basic distance equation.\r<BR>\n" );
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document.write( "Train A setup:<BR>\n" );
document.write( "D = 640 - distance travelled by Train B<BR>\n" );
document.write( "R = x<BR>\n" );
document.write( "T = 4 hrs when it passes Train B coming from the opposite direction.\r<BR>\n" );
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document.write( "Train B setup:<BR>\n" );
document.write( "D = 640 - distance travelled by Train A<BR>\n" );
document.write( "R = x - 20<BR>\n" );
document.write( "T = 3 hrs when it passes Train A coming from the opposite direction\r<BR>\n" );
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document.write( "(i) Speed of Train B = x - 20\r<BR>\n" );
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document.write( "(ii) Distance travelled by Train A = 4x\r<BR>\n" );
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document.write( "Since the moment they pass each other they have covered the 640 km distance.  We can take our solution farther by substituting what we know.\r<BR>\n" );
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document.write( "4x + 3(x-20) = 640<BR>\n" );
document.write( "4x + 3x - 60 = 640<BR>\n" );
document.write( "7x = 700<BR>\n" );
document.write( "x = 100\r<BR>\n" );
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document.write( "So Train A is going 100 km/hr.\r<BR>\n" );
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document.write( "We are told Train B is going 20 km/hr slower, so it is going 80.\r<BR>\n" );
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document.write( "We can check the solution by substituting these values.  And we can calculate answers to questions that have not (yet) been asked.\r<BR>\n" );
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document.write( "Train A ran 100 km/hr for 4 hrs, so it had travelled 400 km at the moment it passed Train B.<BR>\n" );
document.write( "Train B ran 80 km/hr for 3 hrs, so it travelled 240 km at the moment it passed Train A.<BR>\n" );
document.write( "When they pass each other, their combined distance travelled logically has to be 640, which it is.\r<BR>\n" );
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document.write( "So, we're done. </SPAN>\n" );
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