document.write( "Question 179410: The Hudson River flows at a rate of 5 miles per hour. A patrol boat travels 40 miles upriver, and returns in a total time of 6 hours. What is the speed of the boat in still water? \n" ); document.write( "
Algebra.Com's Answer #134382 by MissionPossible(18)\"\" \"About 
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the speed of the boat in still water = V (mile/hour)
\n" ); document.write( "Time = T
\n" ); document.write( "distance(D) = V*T or T = D/V\r
\n" ); document.write( "\n" ); document.write( "upriver the speed would be V-5
\n" ); document.write( "downriver the speed would be V+5\r
\n" ); document.write( "\n" ); document.write( " T = D/V
\n" ); document.write( "upriver Tup = 40/(v-5)
\n" ); document.write( "donwriver Tdown = 40/(v+5)
\n" ); document.write( "Tup + Tdown = 6
\n" ); document.write( "40/(v-5) + 40/(v+5) = 6
\n" ); document.write( "[40(v+5) + 40(v-5)]/[(v+5)(v-5)] = 6
\n" ); document.write( "40V+ 200 + 40V -200 = 6[(v+5)(v-5)]
\n" ); document.write( "80V = 6 (V^2-25)
\n" ); document.write( "80V = 6V^2 - 150
\n" ); document.write( "0 = 6V^2 - 80V - 150
\n" ); document.write( "(6V+10)(V-15) = 0
\n" ); document.write( "V = -10/6 , 15 choose only the positive value (15)
\n" ); document.write( "Then V = 15 miles/hour
\n" ); document.write( "the speed of the boat in still water = 15 mile/hour
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