document.write( "Question 60115This question is from textbook Elementry and Intermediate Algebra
\n" ); document.write( ": 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 #41377 by ankor@dixie-net.com(22740)\"\" \"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( "Since we are dealing in mph, change 20 min to hrs: 20/60 = 1/3 hr
\n" ); document.write( ":
\n" ); document.write( "Let s = her speed in still water
\n" ); document.write( "Then (s+4) = her speed down-stream
\n" ); document.write( "And (s-4) = her speed up-stream
\n" ); document.write( ":
\n" ); document.write( "Time = dist/speed
\n" ); document.write( ":
\n" ); document.write( "Time to go upstream - (1/3) hr = time to go down stream
\n" ); document.write( "\"5%2F%28s-4%29+-+1%2F3+=+5%2F%28s%2B4%29\"
\n" ); document.write( ":
\n" ); document.write( "Mult equation with the common denominator; 3(x-4)(s+4), resulting in:
\n" ); document.write( "3(s+4)(5) - 1(s+4)(s-4) = 3(s-4)(5)
\n" ); document.write( ":
\n" ); document.write( "3(5s + 20) - 1(s^2 - 16) = 3(5s - 20)
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\n" ); document.write( "15s + 60 - s^2 + 16 = 15s - 60
\n" ); document.write( ":
\n" ); document.write( "-s^2 + 15s - 15s = -60 - 60 - 16
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\n" ); document.write( "-s^2 = - 136
\n" ); document.write( ":
\n" ); document.write( "s^2 = 136
\n" ); document.write( ":
\n" ); document.write( "s = SqRt(136)
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\n" ); document.write( "s = 11.66 mph in still water
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\n" ); document.write( "Check using time equation:
\n" ); document.write( "5/7.66 - .33 = 1/15.66
\n" ); document.write( " .65 - .33 = .32 \n" ); document.write( "
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