document.write( "Question 414524: a motorboat took 2 hours to make a downstream trip witha 5 mph current. the return trip against the same current too 4 hours. find the speed of the boat in still water. \n" ); document.write( "

Algebra.Com's Answer #290755 by josmiceli(19441) $\"\"$ $\"About$

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Let $\"s\"$ = the speed of the boat in still water in mi/hr
\n" ); document.write( "Let $\"d\"$ = the one-way trip in miles
\n" ); document.write( "Going downstream, speed = $\"s+%2B+5\"$ mi/hr
\n" ); document.write( "Going upstream, speed = $\"s+-+5\"$ mi/hr
\n" ); document.write( "given:
\n" ); document.write( "downstream:
\n" ); document.write( " $\"d+=+%28s+%2B+5%29%2A2\"$
\n" ); document.write( "upstream:
\n" ); document.write( " $\"d+=+%28s+-+5%29%2A4\"$
\n" ); document.write( "--------------
\n" ); document.write( " $\"d\"$ is the same in both equations
\n" ); document.write( " $\"%28s+%2B+5%29%2A2+=+%28s+-5%29%2A4\"$
\n" ); document.write( " $\"2s+%2B+10+=+4s+-+20\"$
\n" ); document.write( " $\"2s+=+30\"$
\n" ); document.write( " $\"s+=+15\"$
\n" ); document.write( "The speed of the boat in still water is 15 mi/hr
\n" ); document.write( "check:
\n" ); document.write( " $\"d+=+%2815+%2B+5%29%2A2\"$
\n" ); document.write( " $\"d+=+40\"$
\n" ); document.write( "upstream:
\n" ); document.write( " $\"d+=+%2815+-+5%29%2A4\"$
\n" ); document.write( " $\"d+=+40\"$
\n" ); document.write( "OK \n" ); document.write( "

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