document.write( "Question 780612: Jane took 30 min to drive her boat upstream to water-ski at her favorite spot. Coming back later in the day, at the same boat speed, took her 10 min. If the current in that part of the river is 5 km per hr, what was her boat speed in still water? \n" ); document.write( "

Algebra.Com's Answer #475661 by josmiceli(19441) $\"\"$ $\"About$

You can put this solution on YOUR website!
Let $\"+s+\"$ = the speed of the boat in km/hr in still water
\n" ); document.write( "Let $\"+d+\"$ = the one-way distance the boat travels in km
\n" ); document.write( "Going upstream:
\n" ); document.write( " $\"+d+=+%28+s+-+5+%29%2A%281%2F2%29+\"$
\n" ); document.write( "Going downstream:
\n" ); document.write( " $\"+d+=+%28+s+%2B+5%29%2A%2810%2F60%29+\"$
\n" ); document.write( "----------------------
\n" ); document.write( "By substitution:
\n" ); document.write( " $\"+%28+s+-+5+%29%2A%281%2F2%29++=++%28+s+%2B+5%29%2A%281%2F6%29+\"$
\n" ); document.write( "Multiply both sides by $\"+6+\"$
\n" ); document.write( " $\"+3%2A%28+s+-+5+%29+=+s+%2B+5+\"$
\n" ); document.write( " $\"+3s+-+15+=+s+%2B+5+\"$
\n" ); document.write( " $\"+2s+=+20+\"$
\n" ); document.write( " $\"+s+=+10+\"$
\n" ); document.write( "The speed of the boat in still water is 10 km/hr
\n" ); document.write( "check:
\n" ); document.write( " $\"+d+=+%28+s+-+5+%29%2A%281%2F2%29+\"$
\n" ); document.write( " $\"+d+=+%28+10+-+5+%29%2A%281%2F2%29+\"$
\n" ); document.write( " $\"+d+=+5%2F2+\"$ km
\n" ); document.write( "and
\n" ); document.write( " $\"+d+=+%28+s+%2B+5%29%2A%281%2F6%29+\"$
\n" ); document.write( " $\"+d+=+%28+10+%2B+5+%29%2A%281%2F6%29+\"$
\n" ); document.write( " $\"+d+=+15%2F6+\"$
\n" ); document.write( " $\"+d+=+5%2F2+\"$ km
\n" ); document.write( "OK
\n" ); document.write( " \n" ); document.write( "

\n" );