document.write( "Question 195539: Adriana's 18-kilometer boat trip downriver took two hours, but the return trip back upstream took three hours. Figure the speed of the boat in still water and the speed of the current of the river. \n" ); document.write( "
Algebra.Com's Answer #146659 by anantha(86)\"\" \"About 
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sol:
\n" ); document.write( "speed of the boat in still water= x km/h
\n" ); document.write( "speed of the current= y km/h
\n" ); document.write( "down stream speed=(x+y) km/h
\n" ); document.write( "up stream speed=(x-y) km/h
\n" ); document.write( "time=distance/speed
\n" ); document.write( "according to the problem
\n" ); document.write( "total distance=18 km
\n" ); document.write( "speed of the boat in down stream=(x+y) km/h
\n" ); document.write( "time taken down stream=2hours\r
\n" ); document.write( "\n" ); document.write( "distance/speed of down stream= 2h
\n" ); document.write( "18/(x+y)=2
\n" ); document.write( "multiplying by (x+y) on both sides
\n" ); document.write( "18
\n" ); document.write( "------ *(x+y)=2*(x+y)
\n" ); document.write( "(x+y)
\n" ); document.write( "18=2(x+y)
\n" ); document.write( "time taken up stream=3hours
\n" ); document.write( "distance/speed of upstream=3h
\n" ); document.write( "18/(x-y)=3
\n" ); document.write( "multiplying by (x-y) on both sides
\n" ); document.write( "18
\n" ); document.write( "------ *(x-y)=3*(x-y)
\n" ); document.write( "(x-y)
\n" ); document.write( "18=3(x-y)
\n" ); document.write( "2(x+y)=18
\n" ); document.write( "dividing by 2 on both sides
\n" ); document.write( "2(x+y)/2=18/2
\n" ); document.write( "x+y=9 -----(1) equation
\n" ); document.write( "3(x-y)=18
\n" ); document.write( "dividing by 3 on both sides
\n" ); document.write( "3(x-y)/3=18/3
\n" ); document.write( "x-y=6 ----(2) equation
\n" ); document.write( "solving 1 and 2 equations
\n" ); document.write( "x+y=9
\n" ); document.write( "x-y=6
\n" ); document.write( "------
\n" ); document.write( "2x=15
\n" ); document.write( "dividing by 2 on both sides
\n" ); document.write( "2x/2=15/2
\n" ); document.write( "x=7.5
\n" ); document.write( "substitute in 1 st equation
\n" ); document.write( "x+y=9
\n" ); document.write( "7.5+y=9
\n" ); document.write( "subtracting 7.5 on both sides
\n" ); document.write( "7.5+y-7.5=9-7.5
\n" ); document.write( "y=9-7.5
\n" ); document.write( "y=1.5
\n" ); document.write( "speed of the boat in still water=7.5 km/h
\n" ); document.write( "speed of current=1.5 km/h\r
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