document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=1134751>Question 1134751</A>: <I><SPAN STYLE=\"word-break: break-all;\"> Seismographs can record two types of wave energy (P waves and S waves) that travel through the Earth after an earthquake. Traveling through granite, P waves travel approximately 5 km/sec and S waves travel approximately 3 km/sec. If a geologist working at a seismic station measures a time difference of 40 sec between an earthquake's P waves and S waves, how far from the epicenter of the earthquake is the station? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #752230 by </B><A HREF=/tutors/aboutme.mpl?userid=ikleyn><B>ikleyn(52781)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=ikleyn><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=ikleyn><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=752230\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> .\r<BR>\n" );
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document.write( "&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;Another way to solve the problem is <U>THIS</U> :\r<BR>\n" );
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document.write( "Let \"d\" be the distance from the epicenter of the earthquake to the station, in kilometers.\r\n" );
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document.write( "Then the \"time\" equation is\r\n" );
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document.write( "    <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=d%2F3 ALIGN=MIDDLE  ALT=\"d%2F3\"   DISABLED_style= \"max-width:90%; height:auto;\" > - <IMG STYLE=\"max-width:80%;\" SRC=/cgi-bin/plot-formula.mpl?expression=d%2F5 ALIGN=MIDDLE  ALT=\"d%2F5\"   DISABLED_style= \"max-width:90%; height:auto;\" > = 40    seconds.\r\n" );
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document.write( "To solve it, multiply both sides by 15.  You will get\r\n" );
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document.write( "    5d - 3d = 40*15\r\n" );
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document.write( "    2d = 600 \r\n" );
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document.write( "    d = 600/2 = 300 kilometers.      <U>ANSWER</U>\r\n" );
document.write( "</PRE>\r<BR>\n" );
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document.write( "Solved.\r<BR>\n" );
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document.write( "----------------\r<BR>\n" );
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document.write( "The lesson to learn from my post is <U>THIS</U> :\r<BR>\n" );
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document.write( "    Learn on how to write the \"time\" equation\r\n" );
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document.write( "    and how to solve it.\r\n" );
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document.write( "The benefit of this approach is in that the equation from the very beginning is written for the unknown value (distance)\r<BR>\n" );
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document.write( "and does not introduce an intermediate variable \"t\" (time).\r<BR>\n" );
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document.write( "In school, the traditional method is solving such problems using time.\r<BR>\n" );
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document.write( "But a professional way and a method is to write the \"time\" equation for the unknown distance  from the very beginning\r<BR>\n" );
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document.write( "and to get the distance from this equation without using the intermediate variable \"t\".\r<BR>\n" );
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document.write( "Ideally when you know and can use EITHER of these two methods.\r<BR>\n" );
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document.write( "===============\r<BR>\n" );
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document.write( "See the lesson\r<BR>\n" );
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document.write( "&nbsp;&nbsp;&nbsp;&nbsp;- <A  rel=nofollow HREF=https://www.algebra.com/algebra/homework/word/travel/Earthquake-waves.lesson>Earthquake waves</A> \r<BR>\n" );
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document.write( "int his site with the solution to similar problem.\r<BR>\n" );
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document.write( "By the way, at an interview it is very easy test to distinct a professional solver from an \"amateur\".\r<BR>\n" );
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document.write( "An \"amateur\" will solve such problem using time.\r<BR>\n" );
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document.write( "A professional solver will use the time equation as I explained it above.\r<BR>\n" );
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document.write( " </SPAN>\n" );
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