document.write( "Question 1107789: Jane took 30 min to drive her boat upstream to water-ski at her favorite spot. Coming back later in the day, at the same boat speed, took her 15 min. If the current in that part of the river is 6 km per hr, what was her boat speed in still water? \n" ); document.write( "

Algebra.Com's Answer #853842 by ikleyn(53619) $\"\"$ $\"About$

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\n" ); document.write( "Jane took 30 min to drive her boat upstream to water-ski at her favorite spot.
\n" ); document.write( "Coming back later in the& day, at the same boat speed, took her 15 min.
\n" ); document.write( "If the current in that part of the river is 6 km per hr, what was her boat speed in still water?
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document.write( "Let boat speed in still water be x\r\n" );
document.write( "The speed of the current = 6 km/h\r\n" );
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document.write( "upstream speed = (x-6) km/h.\r\n" );
document.write( "downstream speed = (x+6) km/h\r\n" );
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document.write( "distance = time * speed\r\n" );
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document.write( "Distance upstream is  1/2 of an hour * (x-6) km/h\r\n" );
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document.write( "    d =  kilometers.\r\n" );
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document.write( "Distance downstream is  1/4 of an hour * (x+6) km/h\r\n" );
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document.write( "    d =  kilometers.\r\n" );
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document.write( "The distance is the same in both directions - - - so, we have this equation \r\n" );
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document.write( "     =      (1)\r\n" );
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document.write( "Multiply equation (1) by 4  (both sides).  We get\r\n" );
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document.write( "    2(x-6) = x + 6,\r\n" );
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document.write( "    2x - 12 = x + 6,\r\n" );
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document.write( "    2x - x = 12 + 6,\r\n" );
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document.write( "       x   =    18.\r\n" );
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document.write( "ANSWER.  The speed of boat in still water is 18 km/h.\r\n" );
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