document.write( "Question 325572: A boat went 10km upstream against the current then turned around and went 15km downstream with current. The current speed was 3km/hour and upstream trip took 30 minutes longer. What was the speed of the boat without the speed of the current? \n" ); document.write( "
Algebra.Com's Answer #233123 by mananth(16946)\"\" \"About 
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10km upstream against the current
\n" ); document.write( "15km downstream with current.
\n" ); document.write( "current speed was 3km/hour
\n" ); document.write( "upstream trip took 30 minutes longer.
\n" ); document.write( "..
\n" ); document.write( "let speed in still water be x km/hour
\n" ); document.write( "..
\n" ); document.write( "downstream speed = x+3 km/hour
\n" ); document.write( "15 km distance.
\n" ); document.write( "time taken = 15/ x+3
\n" ); document.write( "..
\n" ); document.write( "upstream speed will be x-3 km/hour
\n" ); document.write( "distance 10 km.
\n" ); document.write( "time taken = 10/x-3
\n" ); document.write( "..
\n" ); document.write( "upstream time - downstream time = 1/2 hour
\n" ); document.write( "10/ x-3 - 15/ x+3 =1/2
\n" ); document.write( "LCM of left side
\n" ); document.write( "(x+3)(x-3)
\n" ); document.write( "10(x+3)-15(x-3)/ (x+3)(x-3)= 1/2
\n" ); document.write( "10x+30-15x+45=1/2 * (x+3)(x-3)
\n" ); document.write( "-5x+75= 1/2 * x^2-9
\n" ); document.write( "2(-5x+75)=x^2-9
\n" ); document.write( "-10x+150=x^2-9
\n" ); document.write( "x^2+10x-159=0\r
\n" ); document.write( "\n" ); document.write( "..
\n" ); document.write( "the roots of the equation x1 , x2 will be
\n" ); document.write( "x1= (-10+sqrt(100+636) )/2
\n" ); document.write( "x1=-18.56 since it is negative ignore.
\n" ); document.write( "x2=(-10-sqrt(100+636) )/2
\n" ); document.write( "x2= 8.56 km/hr the speed of boat in still water \n" ); document.write( "
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