document.write( "Question 754313: A boat can travel at a speed of 12 km/h in still water. If it takes three hours to go
\n" ); document.write( "15 km upstream and back, find the speed of the current, giving your answer
\n" ); document.write( "correct to 2 decimal places. \n" ); document.write( "

Algebra.Com's Answer #458989 by lwsshak3(11628) $\"\"$ $\"About$

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A boat can travel at a speed of 12 km/h in still water. If it takes three hours to go
\n" ); document.write( "15 km upstream and back, find the speed of the current, giving your answer
\n" ); document.write( "correct to 2 decimal places.
\n" ); document.write( "***
\n" ); document.write( "let x=speed of current
\n" ); document.write( "12+x =speed of boat downstream
\n" ); document.write( "12-x =speed of boat upstream
\n" ); document.write( "travel time=distance/speed
\n" ); document.write( "..
\n" ); document.write( " $\"15%2F%2812%2Bx%29%2B15%2F%2812-x%29=3\"$
\n" ); document.write( "LCD: (12+x)(12-x)
\n" ); document.write( " $\"15%2812-x%29%2B15%2812%2Bx%29=3%28144-x%5E2%29\"$
\n" ); document.write( "180-15x+180+15x=432-3x^2
\n" ); document.write( "3x^2-72=0
\n" ); document.write( "x^2-24=0
\n" ); document.write( "x^2=24
\n" ); document.write( "x=-√24 (reject, x>0)
\n" ); document.write( "or
\n" ); document.write( "x=√24≈4.90
\n" ); document.write( "speed of current≈4.90 km/h
\n" ); document.write( " \n" ); document.write( "

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