document.write( "<A HREF=/cgi-bin/jump-to-question.mpl?question=151181>Question 151181</A>: <I><SPAN STYLE=\"word-break: break-all;\"> a motorboat can go 8 miles downstream in 20 minutes.  It takes the same motorboat 30 minutes to go back upstream the same 8 miles.  find the speed of the current. </SPAN>\n" );
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document.write( "a motorboat can go 8 miles downstream in 20 minutes.  It takes the same motorboat 30 minutes to go back upstream the same 8 miles.  find the speed of the current.<BR>\n" );
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document.write( "Let m = speed of motorboat<BR>\n" );
document.write( "and c = speed of current<BR>\n" );
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document.write( "When going downstream, current speed is added to boat speed -- and, the total speed is \"8 miles downstream in 20 minutes\"<BR>\n" );
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document.write( "To convert to \"miles per hour\" we multiply by 60 mins per 1 hour:<BR>\n" );
document.write( "(8 miles/20 mins) * (60 mins/1 hour) = 24 mph<BR>\n" );
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document.write( "This gives us our first equation (1):<BR>\n" );
document.write( "m+c = 24<BR>\n" );
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document.write( "When going upstream, the boat speed is reduced by the current -- and, the total speed is \"8 miles in 30 minutes\".<BR>\n" );
document.write( "To convert to \"miles per hour\" we multiply by 60 mins per 1 hour:<BR>\n" );
document.write( "(8 miles/30 mins) * (60 mins/1 hour) = 16 mph<BR>\n" );
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document.write( "This gives us our second equation (2):<BR>\n" );
document.write( "m-c = 16<BR>\n" );
document.write( "m = 16+c<BR>\n" );
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document.write( "Plug the above into equation 1 and solve for c:<BR>\n" );
document.write( "m+c = 24<BR>\n" );
document.write( "16+c+c = 24<BR>\n" );
document.write( "16+2c = 24<BR>\n" );
document.write( "2c = 8<BR>\n" );
document.write( "c = 4 mph\r<BR>\n" );
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document.write( " </SPAN>\n" );
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