document.write( "Question 676243: a boat traveled 72 miles downstream and back. The trip downstream took 3 hours. The trip back took 18 hours. Find the speed of the boat in still water and the speed of the current. \n" ); document.write( "
Algebra.Com's Answer #420263 by ankor@dixie-net.com(22740)\"\" \"About 
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a boat traveled 72 miles downstream and back.
\n" ); document.write( " The trip downstream took 3 hours. The trip back took 18 hours.
\n" ); document.write( " Find the speed of the boat in still water and the speed of the current.
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\n" ); document.write( "Let s = boat speed in still water
\n" ); document.write( "let c = speed of the current
\n" ); document.write( "Then
\n" ); document.write( "(s+c) = effective speed downstream
\n" ); document.write( "and
\n" ); document.write( "(s-c) = effective speed upstream
\n" ); document.write( ":
\n" ); document.write( "Write a distance equation for each way; dist = time * speed
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\n" ); document.write( "3(s+c) = 72
\n" ); document.write( "18(s-c) = 72
\n" ); document.write( "Simplify both equations, divide the 1st by 3 and the 2nd by 18 and you have
\n" ); document.write( "s + c = 24
\n" ); document.write( "s - c = 4
\n" ); document.write( "------------- adding equations eliminates c, find s
\n" ); document.write( "2s = 28
\n" ); document.write( "s = 28/2
\n" ); document.write( "s = 14 mph, boat speed in still water
\n" ); document.write( ":
\n" ); document.write( "I'll let you find the speed of the current
\n" ); document.write( "Check your solution in the original equations \n" ); document.write( "
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