document.write( "Question 553486: A boat makes a 120-mile trip downstream in 3 hours but makes the return trip in 4 hours. What is the rate of the current? \n" ); document.write( "

Algebra.Com's Answer #360882 by josmiceli(19441) $\"\"$ $\"About$

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Let $\"+s+\"$ = the speed of the boat in still water
\n" ); document.write( "Let $\"+c+\"$ = the rate of the current
\n" ); document.write( " $\"+s+%2B+c+\"$ = the speed of the boat going downstream
\n" ); document.write( " $\"+s+-+c+\"$ = the speed of the boat going upstream
\n" ); document.write( "------------
\n" ); document.write( "given:
\n" ); document.write( "Going downstream:
\n" ); document.write( "(1) $\"+120+=+%28+s+%2B+c+%29%2A3+\"$
\n" ); document.write( "Going upstream:
\n" ); document.write( "(2) $\"+120+=+%28+s+-+c+%29%2A4+\"$
\n" ); document.write( "--------------------
\n" ); document.write( "(1) $\"+3s+%2B+3c+=+120+\"$
\n" ); document.write( "(2) $\"+4s+-+4c+=+120+\"$
\n" ); document.write( "--------------------
\n" ); document.write( "(1) $\"+s+%2B+c+=+40+\"$
\n" ); document.write( "(2) $\"+s+-+c+=+30+\"$
\n" ); document.write( "Add the equations
\n" ); document.write( " $\"+2s+=+70+\"$
\n" ); document.write( " $\"+s+=+35+\"$
\n" ); document.write( "and
\n" ); document.write( "(1) $\"+s+%2B+c+=+40+\"$
\n" ); document.write( "(1) $\"+35+%2B+c+=+40+\"$
\n" ); document.write( "(1) $\"+c+=+5+\"$
\n" ); document.write( "The speed of the current is 5 mi/hr \n" ); document.write( "

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