document.write( "Question 840888: a motor boat takes 2 hours more to cover a distance 30 km upstream than it takes to cover the same distance down stream if speed of stream is 2 km/hr then find the speed in still water. \n" ); document.write( "
Algebra.Com's Answer #506476 by hamsanash1981@gmail.com(151)\"\" \"About 
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let the time taken to cover a distance of 30 km be x and then the time taken by up stream will be x+2
\n" ); document.write( "speed of downstream = 30/x
\n" ); document.write( "speed of upstream = 30/x+2
\n" ); document.write( "speed of the stream = (downstream - upstream)/2
\n" ); document.write( " 2 = (30/x-30/x+2)/2
\n" ); document.write( "=> 4 = (30(x+2) -30(x) )/x(x+2)
\n" ); document.write( "4(x(x+2)) = 30(x+2-x)
\n" ); document.write( "4(x^2 + 2x) = 60
\n" ); document.write( "4x^2 + 8x - 60 =0
\n" ); document.write( "divide the above equation by 4
\n" ); document.write( "x^2 +2x - 15 =0
\n" ); document.write( "factorising the equation we get\r
\n" ); document.write( "\n" ); document.write( "(x+5)(x-3)=0
\n" ); document.write( "x= -5 x= 3
\n" ); document.write( "avoiding negative we have the x = 3
\n" ); document.write( "the x +2 = 5\r
\n" ); document.write( "\n" ); document.write( "Speed of the boat in still water = (downstream+upstream)/2
\n" ); document.write( "= (30/3+ 30/5)/2
\n" ); document.write( "= (10+6)/2
\n" ); document.write( "=16/2
\n" ); document.write( "=8 km/hr
\n" ); document.write( " \n" ); document.write( "
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