document.write( "Question 159403: A boat moves 9 kilometers upstream in the same amount of time it moves 19 kilometers downstream. If the rate of the current is 9 kilometers per hour, find the rate of the boat in still water. \n" ); document.write( "
Algebra.Com's Answer #117546 by ankor@dixie-net.com(22740)\"\" \"About 
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boat moves 9 kilometers upstream in the same amount of time it moves 19 kilometers downstream. If the rate of the current is 9 kilometers per hour, find the rate of the boat in still water.
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\n" ); document.write( "Let x = speed in still water
\n" ); document.write( "then
\n" ); document.write( "(x+9) = speed downstream
\n" ); document.write( "and
\n" ); document.write( "(x-9) = speed upstream
\n" ); document.write( ":
\n" ); document.write( "Times of the two trips are equal; write a time equation from this fact:
\n" ); document.write( "Time = \"dist%2Fspeed\"
\n" ); document.write( ":
\n" ); document.write( "Downstream time = Upstream time
\n" ); document.write( "\"19%2F%28%28x%2B9%29%29\" = \"9%2F%28%28x-9%29%29\"
\n" ); document.write( "Cross multiply:
\n" ); document.write( "19(x-9) = 9(x+9)
\n" ); document.write( ":
\n" ); document.write( "19x - 171 = 9x + 81
\n" ); document.write( ":
\n" ); document.write( "19x - 9x = 81 + 171
\n" ); document.write( ":
\n" ); document.write( "10x = 252
\n" ); document.write( "x = \"252%2F10\"
\n" ); document.write( "x = 25.2 km in still water
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\n" ); document.write( "Check solution by confirming the times are equal:
\n" ); document.write( "19/34.2 = .56 hrs
\n" ); document.write( "9/16.2 = .56 hrs \n" ); document.write( "
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