document.write( "Question 159561: Junior's boat will go 15 mph in still water. If he can go 12 miles downstream in the same amount of time it takes to go 9 miles upsteam, then what is the speed of the current? \n" ); document.write( "

Algebra.Com's Answer #117689 by ankor@dixie-net.com(22740) $\"\"$ $\"About$

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Junior's boat will go 15 mph in still water. If he can go 12 miles downstream
\n" ); document.write( " in the same amount of time it takes to go 9 miles upstream, then what is the
\n" ); document.write( " speed of the current?
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\n" ); document.write( "Let the speed of the current = x
\n" ); document.write( "then
\n" ); document.write( "(15+x) = speed downstream
\n" ); document.write( "and
\n" ); document.write( "(15-x) = speed upstream
\n" ); document.write( ":
\n" ); document.write( "The times are give as equal, write a time equation from this fact
\n" ); document.write( "remember; Time = $\"dist%2Fspeed\"$
\n" ); document.write( ":
\n" ); document.write( "Down stream time = Upstream time
\n" ); document.write( " $\"15%2F%28%2815%2Bx%29%29\"$ = $\"9%2F%28%2815-x%29%29\"$
\n" ); document.write( "Cross multiply, solve for x
\n" ); document.write( "9(15+x) = 15(15-x)
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\n" ); document.write( "135 + 9x = 225 - 15x
\n" ); document.write( ":
\n" ); document.write( "9x + 15x = 225 - 135
\n" ); document.write( ":
\n" ); document.write( "24x = 90
\n" ); document.write( "x = $\"90%2F24\"$
\n" ); document.write( "x = 3.75 mph is the speed of the current
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\n" ); document.write( "Check solution by finding the times of each trip (add & subtract the current)
\n" ); document.write( "15/18.75 = .8 hrs
\n" ); document.write( "9/11.25 = .8 hrs, confirms our solution \n" ); document.write( "

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