document.write( "Question 154886: A cruise boat travels 48 miles downstream in 3 hours and returns upstream in 6 hours. Find the rate of the stream. \n" ); document.write( "
Algebra.Com's Answer #114106 by orca(409)\"\" \"About 
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Let x be the speed of the boat in still water.
\n" ); document.write( "Let y be the speed of the current of the river.
\n" ); document.write( "Then
\n" ); document.write( "the boat's downstream speed relative to the river bank is x + y,
\n" ); document.write( "the boat's upstream speed relative to the river bank is x - y.
\n" ); document.write( "As the boat travels 48 miles downstream in 3 hours, we have
\n" ); document.write( "3(x+y)=48 ...............(1)
\n" ); document.write( "As the boat travels 48 miles upstream in 6 hours, we have
\n" ); document.write( "6(x-y)=48 ................(2)
\n" ); document.write( "Simplifying equation (1) and (2) by dividing them by 3 and 6 respectively, we have
\n" ); document.write( "x+y=16 ........(3)
\n" ); document.write( "x-y=8 ........(4)
\n" ); document.write( "Adding (3) and (4) together, we have
\n" ); document.write( "2x = 24
\n" ); document.write( "So x = 12
\n" ); document.write( "Substituting x = 12 into (3), we obtain
\n" ); document.write( "12 + y = 16
\n" ); document.write( "Solving for y, we get
\n" ); document.write( "y = 4
\n" ); document.write( "So the speed of the river is 4 miles per hour.\r
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