document.write( "Question 687746: Please help. The Columbia River flows at a rate of 2mph for the length of a popular boating route. In order for a motorized dinghy to travel 3 mi upriver and then return in a total of 4 hrs, how fast must the boat be able to travel in still water? \n" ); document.write( "
Algebra.Com's Answer #425324 by stanbon(75887)\"\" \"About 
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The Columbia River flows at a rate of 2mph for the length of a popular boating route. In order for a motorized dinghy to travel 3 mi upriver and then return in a total of 4 hrs, how fast must the boat be able to travel in still water?
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\n" ); document.write( "Upriver DATA:
\n" ); document.write( "distance = 3 miles ; rate = b-2 mph ; time = d/r = 3(b-2) hrs
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\n" ); document.write( "Downriver DATA:
\n" ); document.write( "distance = 3 miles ; rate + b+2 mph ; time = d/r = 3/(b+2) hrs
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\n" ); document.write( "Equation:
\n" ); document.write( "time + time = 4 hrs
\n" ); document.write( "3/(b-2) + 3/(b+2) = 4
\n" ); document.write( "3(b+2) + 3(b-2) = 4(b^2-4)
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\n" ); document.write( "6b = 4b^2 -16
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\n" ); document.write( "2b^2 - 3b - 8 = 0
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\n" ); document.write( "b = [3 +- sqrt(9-4*2*-8)]/4
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\n" ); document.write( "Positive solution:
\n" ); document.write( "b = [3 + sqrt(73)]/4
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\n" ); document.write( "b = 2.89 mph (speed of the boat in still water)
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\n" ); document.write( "Cheers,
\n" ); document.write( "Stan H.
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