document.write( "Question 720809: Don Williams uses his small motorboat to go 4 miles upstream to his favorite fishing spot. Against the current, the trip takes 2/5 hours. With the current the trip takes 1/5. How fast can the boat travel in still water. What is the speed of the current?? thanks \n" ); document.write( "
Algebra.Com's Answer #441988 by josmiceli(19441)\"\" \"About 
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Let \"+s+\" = the speed of the boat in still water
\n" ); document.write( "Let \"+c+\" = the speed of ther current
\n" ); document.write( "\"+s+-+c+\" = the speed of the boat going against the current
\n" ); document.write( "\"+s+%2B+c+\" = the speed of the boat going with the current
\n" ); document.write( "-----------------
\n" ); document.write( "Going upstream:
\n" ); document.write( "(1) \"+4+=+%28+s+-+c+%29%2A%282%2F5%29+\"
\n" ); document.write( "Going downstream:
\n" ); document.write( "(2) \"+4+=+%28+s+%2B+c+%29%2A%281%2F5%29+\"
\n" ); document.write( "----------------------
\n" ); document.write( "(1) \"+20+=+2s+-+2c+\"
\n" ); document.write( "(1) \"+10+=+s+-+c+\"
\n" ); document.write( "and
\n" ); document.write( "(2) \"+20+=+s+%2B+c+\"
\n" ); document.write( "----------------
\n" ); document.write( "Add (1) and (2)
\n" ); document.write( "\"+30+=+2s+\"
\n" ); document.write( "\"+s+=+15+\"
\n" ); document.write( "and
\n" ); document.write( "(1) \"+10+=+s+-+c+\"
\n" ); document.write( "(1) \"+10+=+15+-+c+\"
\n" ); document.write( "(1) \"+c+=+15+-+10+\"
\n" ); document.write( "(1) \"+c+=+5+\"
\n" ); document.write( "The speed of the boat in still water is 15 mi/hr
\n" ); document.write( "The speed of ther current is 5 mi/hr
\n" ); document.write( "check:
\n" ); document.write( "(2) \"+4+=+%28+s+%2B+c+%29%2A%281%2F5%29+\"
\n" ); document.write( "(2) \"+4+=+%28+15+%2B+5+%29%2A%281%2F5%29+\"
\n" ); document.write( "(2) \"+4+=+20%2F5+\"
\n" ); document.write( "(2) \"+4+=+4+\"
\n" ); document.write( "OK
\n" ); document.write( "(1) \"+4+=+%28+s+-+c+%29%2A%282%2F5%29+\"
\n" ); document.write( "(1) \"+4+=+%28+15+-+5+%29%2A%282%2F5%29+\"
\n" ); document.write( "(1) \"+4+=+20%2F5+\"
\n" ); document.write( "(10 \"+4+=+4+\"
\n" ); document.write( "OK\r
\n" ); document.write( "
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