document.write( "Question 162798: Debbie traveled by boat 5 miles upstream to fish in her favorite spot. Because of the 4-mph current, it took her 20 minutes longer to get there than to return. How fast will her boat go in still water? \n" ); document.write( "
Algebra.Com's Answer #120010 by nerdybill(7384)\"\" \"About 
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Debbie traveled by boat 5 miles upstream to fish in her favorite spot. Because of the 4-mph current, it took her 20 minutes longer to get there than to return. How fast will her boat go in still water?
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\n" ); document.write( "Let t = time going upstream (with current)
\n" ); document.write( "and b = speed of boat in still waters
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\n" ); document.write( "from: \"Debbie traveled by boat 5 miles upstream to fish in her favorite spot.\"
\n" ); document.write( "5 = t(b+4)
\n" ); document.write( "from: \"Because of the 4-mph current, it took her 20 minutes longer to get there than to return.\"
\n" ); document.write( "5 = (t + 1/3)(b-4)
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\n" ); document.write( "5 = t(b+4)
\n" ); document.write( "t = 5/(b+4)
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\n" ); document.write( "Substitute the above into equation 2:
\n" ); document.write( "5 = (t + 1/3)(b-4)
\n" ); document.write( "5 = (5/(b+4) + 1/3)(b-4)
\n" ); document.write( "15(b+4) = (15 + (b+4))(b-4)
\n" ); document.write( "15(b+4) = (b+19)(b-4)
\n" ); document.write( "15b+60 = b^2-4b+19b-76
\n" ); document.write( "15b+60 = b^2+15b-76
\n" ); document.write( "60 = b^2-76
\n" ); document.write( "136 = b^2
\n" ); document.write( "11.662 mph = b (speed of boat in still water)\r
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