document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=68525>Question 68525</A>This question is from textbook <A HREF=http://www.amazon.com/exec/obidos/ASIN/0395430526/algebrahomeworkh>Algebra:Structure and Method</A><BR>\n" );
document.write( ": <I><SPAN STYLE=\"word-break: break-all;\"> If I increase my usual driving speed by 10 km/h, I can drive the 255 km trip to Nashville in 24 min less than usual. How fast do I usually drive? </SPAN>\n" );
document.write( "</I><HR><TABLE width=100%><TR><TD><B><A HREF=http://www.algebra.com/>Algebra.Com's</A> Answer #48774 by </B><A HREF=/tutors/aboutme.mpl?userid=ptaylor><B>ptaylor(2198)</B></A><img src=\"/images/stars/stars-13.gif\" alt=\"\" >&nbsp;<A HREF=/tutors/aboutme.mpl?userid=ptaylor><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=ptaylor><BR>You can <A HREF=\"/cgi-bin/embed-solution.mpl?show=1&solution=48774\">put this solution on YOUR website!</A><BR><SPAN STYLE=\"word-break: break-all;\"> Let x=usual driving speed\r<BR>\n" );
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document.write( "Then x+10=increased driving speed\r<BR>\n" );
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document.write( "Distance(d)=rate(r) times time(t) or d=rt and t=d/r\r<BR>\n" );
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document.write( "Time it takes at usual driving speed=255/x\r<BR>\n" );
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document.write( "Time it takes at increased speed=255/(x+10)\r<BR>\n" );
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document.write( "24 min=24/60 hr=0.4 hr<BR>\n" );
document.write( "Now we are told that increased driving time plus 0.4 hr equals usual driving time.  So our equation to solve is:\r<BR>\n" );
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document.write( " 255/(x+10)+0.4=255/x   multiply both sides by x(x+10)  \r<BR>\n" );
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document.write( "255(x)(x+10)/(x+10)+(0.4)(x)(x+10)=255/(x+10)(x/x)  clear fractions\r<BR>\n" );
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document.write( "255x+0.4x^2+4x=255x+2550  subtract 255x and 2550 from both sides\r<BR>\n" );
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document.write( "0.4x^2+4x-2550=0  divide by 0.4<BR>\n" );
document.write( "x^2+10x-6375=0----------------------quadratic in standard form\r<BR>\n" );
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document.write( "This quadratic can be factored\r<BR>\n" );
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document.write( "(x+85)(x-75)=0\r<BR>\n" );
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document.write( "x=-85 km/h-----------------discount negative speed<BR>\n" );
document.write( "and<BR>\n" );
document.write( "x=75 km/h----------------------------usual speed\r<BR>\n" );
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document.write( "x+10=75+10=85 km/h-----------------------increased speed\r<BR>\n" );
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document.write( "ck\r<BR>\n" );
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document.write( "255/75=255/85+0.4<BR>\n" );
document.write( "3.4=3.4\r<BR>\n" );
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document.write( "Hope this helps----ptaylor </SPAN>\n" );
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