document.write( "Question 462476: A boat can go 63 mph in still water. It takes as long to go 120 miles upstream as it does to go 150 miles downstream. What is the current? \n" ); document.write( "

Algebra.Com's Answer #317065 by josmiceli(19441) $\"\"$ $\"About$

You can put this solution on YOUR website!
Let $\"+c+\"$ = speed of current
\n" ); document.write( "Let $\"+t+\"$ = time to go either upstream or downstream
\n" ); document.write( "given:
\n" ); document.write( "Speed in still water = $\"+63+\"$ mi/hr
\n" ); document.write( "Going upstream, speed = $\"+63+-+c+\"$
\n" ); document.write( "Going downstream, speed = $\"+63+%2B+c+\"$
\n" ); document.write( "Upstream:
\n" ); document.write( "(1) $\"+120+=+%2863+-+c%29%2At+\"$
\n" ); document.write( "Downstream:
\n" ); document.write( "(2) $\"+150+=+%2863+%2B+c%29%2At+\"$
\n" ); document.write( "Add the equations
\n" ); document.write( " $\"+120+%2B+150+=+%2863-c%29%2At+%2B+%2863%2Bc%29%2At+\"$
\n" ); document.write( " $\"+270+=+63t+-+c%2At+%2B+63t+%2B+c%2At+\"$
\n" ); document.write( " $\"+270+=+126t+\"$
\n" ); document.write( " $\"+t+=+2.143+\"$ hrs
\n" ); document.write( "Substitute in (2)
\n" ); document.write( "(2) $\"+150+=+%2863+%2B+c%29%2A2.143+\"$
\n" ); document.write( "(2) $\"+150+=+135+%2B+2.143c+\"$
\n" ); document.write( "(2) $\"+2.143c+=+15+\"$
\n" ); document.write( "(2) $\"+c+=+7+\"$
\n" ); document.write( "The speed of the current is 7 mi/hr
\n" ); document.write( "check:
\n" ); document.write( "(1) $\"+120+=+%2863+-+7%29%2A2.143+\"$
\n" ); document.write( "(1) $\"+120+=+56%2A2.143+\"$
\n" ); document.write( "(1) $\"+120+=+120.008+\"$ (rounding off error)
\n" ); document.write( "OK \n" ); document.write( "

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