document.write( "Question 17892: . A boat travels at the speed of 20 Miles per hour in still water. It travels 48 miles up stream, and then returns to the starting point in a total of five hours. The speed of the current is ____ miles per hour. \n" ); document.write( "

Algebra.Com's Answer #8688 by xcentaur(357) $\"\"$ $\"About$

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let the speed of the boat be x = 20 mph
\n" ); document.write( "let the speed of the current be y mph
\n" ); document.write( "

\n" ); document.write( "Then speed up stream = x-y = (20-y) mph
\n" ); document.write( "Distance up=48 miles
\n" ); document.write( "therefore Time[1] = 48/(20-y)
\n" ); document.write( "

\n" ); document.write( "Speed downstream = x+y = (20+y)mph
\n" ); document.write( "Distance=48miles
\n" ); document.write( "Time[2]=48/(20+y)
\n" ); document.write( "

\n" ); document.write( "Total time=5 hours
\n" ); document.write( "total time=48(20+y)+48/(20-y)
\n" ); document.write( " $\"+%2848%2F%2820%2By%29%29%2B%2848%2F%2820-y%29%29=+5+\"$
\n" ); document.write( " $\"+%2848%2820-y%29+%2B+48%2820%2By%29%29%2F%28%2820-y%29%2820%2By%29%29+=+5+\"$
\n" ); document.write( " $\"+48%2820-y%29+%2B+48%2820%2By%29+=+5%2820-y%29%2820%2By%29+\"$
\n" ); document.write( " $\"+2%2A48%2A20+=+5%28400-y%5E2%29+\"$
\n" ); document.write( " $\"+%2848%2A40%29%2F5+=+400+-+y%5E2+\"$
\n" ); document.write( " $\"+1920%2F5+=+400+-+y%5E2+\"$
\n" ); document.write( " $\"+384+=+400+-+y%5E2+\"$
\n" ); document.write( " $\"+384-400+=+-y%5E2+\"$
\n" ); document.write( " $\"+-y%5E2+=+-16+\"$
\n" ); document.write( " $\"+y%5E2+=+16+\"$
\n" ); document.write( "Hence y=plus or minus 4
\n" ); document.write( "Speed of the current in this context cannot be negative,hence
\n" ); document.write( " $\"+y+=+4+\"$
\n" ); document.write( "

\n" ); document.write( "Speed of boat=20 mph
\n" ); document.write( "Speed of current=4 mph
\n" ); document.write( "

\n" ); document.write( "Hope this helps,
\n" ); document.write( "Prabhat \n" ); document.write( "

\n" );