document.write( "Question 804041: The Speed of a river is 7mph. If a boat travels 20 miles downstream in the same time it takes to travel 10 miles upstream, find the speed of the boat in still water?
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Algebra.Com's Answer #484573 by josmiceli(19441) $\"\"$ $\"About$

You can put this solution on YOUR website!
Let $\"+t+\"$ = the time in hours going both
\n" ); document.write( "upstream and downstream
\n" ); document.write( "Let $\"+s+\"$ = the speed of the boat in still water
\n" ); document.write( "-----------------
\n" ); document.write( "Going downstream:
\n" ); document.write( "(1) $\"+20+=+%28+s+%2B+7+%29%2At+\"$
\n" ); document.write( "Going upstream:
\n" ); document.write( "(2) $\"+10+=+%28+s+-+7+%29%2At+\"$
\n" ); document.write( "--------------------
\n" ); document.write( "(1) $\"+20+=+s%2At+%2B+7t+\"$
\n" ); document.write( "and
\n" ); document.write( "(2) $\"+10+=+s%2At+-+7t+\"$
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\n" ); document.write( "Subtract (2) from (1)
\n" ); document.write( "(1) $\"+20+=+s%2At+%2B+7t+\"$
\n" ); document.write( "(2) $\"+-10+=+-s%2At+%2B+7t+\"$
\n" ); document.write( " $\"+10+=+14t+\"$
\n" ); document.write( " $\"+t+=+5%2F7+\"$
\n" ); document.write( "-----------
\n" ); document.write( "(1) $\"+20+=+%28+s+%2B+7+%29%2At+\"$
\n" ); document.write( "(1) $\"+20+=+%28+s+%2B+7+%29%2A%285%2F7%29+\"$
\n" ); document.write( "(1) $\"+140+=+5s+%2B+35+\"$
\n" ); document.write( "(1) $\"+5s+=+105+\"$
\n" ); document.write( "(1) $\"+s+=+21+\"$
\n" ); document.write( "The speed of the boat in still water is 21 mi/hr
\n" ); document.write( "check:
\n" ); document.write( "(2) $\"+10+=+%28+s+-+7+%29%2At+\"$
\n" ); document.write( "(2) $\"+10+=+%28+21+-+7+%29%2A%285%2F7%29+\"$
\n" ); document.write( "(2) $\"+10+=+14%2A%285%2F7%29+\"$
\n" ); document.write( "(2) $\"+70+=+70+\"$
\n" ); document.write( "OK
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