document.write( "Question 668812: A boat moves 28 km/h in still water. It travels 80 km upstream and 80 km downstream in a total time of 7 hours. What is the speed of the current? \n" ); document.write( "
Algebra.Com's Answer #415889 by mananth(16946)\"\" \"About 
You can put this solution on YOUR website!
Boat speed = 28 mph
\n" ); document.write( "current speed = x mph
\n" ); document.write( "
\n" ); document.write( "against current = 28 - x
\n" ); document.write( "with current = 28 + x
\n" ); document.write( "
\n" ); document.write( "Total distance = 80 miles Total Time= 7.00 hours
\n" ); document.write( "Time upstream + time downstream =
\n" ); document.write( "
\n" ); document.write( "80/(28-x)+80/(28+x)= 7
\n" ); document.write( "80(28+x )+80(28 -x)=7(784-X^2)
\n" ); document.write( "2240+80 x+2240 -80x=5488-7X^2
\n" ); document.write( "4480 - -5488 = -7 X^2
\n" ); document.write( "-1008 = -7 X^2
\n" ); document.write( "-7 X^2= -1008
\n" ); document.write( "x^2 = 144
\n" ); document.write( "x = +/- 12
\n" ); document.write( "
\n" ); document.write( "Speed of current = 12 km/h
\n" ); document.write( " \n" ); document.write( "
\n" );