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It took Jeremy and Kirk five hours to canoe 32 miles downstream on the upper Blue River.
\n" ); document.write( " The next day it took them seven hours to canoe upstream for 21 miles.
\n" ); document.write( " What was the speed of the current,
\n" ); document.write( ":
\n" ); document.write( "Let c = the speed of the current
\n" ); document.write( "Let s = canoes speed in still water
\n" ); document.write( "then
\n" ); document.write( "(s-c) = effective speed upstream
\n" ); document.write( "and
\n" ); document.write( "(s+c) = effective speed downstream
\n" ); document.write( ":
\n" ); document.write( "Write a distance equation for each trip: dist = time * effective speed
\n" ); document.write( "5(s+c) = 32
\n" ); document.write( "and
\n" ); document.write( "7(s-c) = 21
\n" ); document.write( "simplify divide both sides by 7
\n" ); document.write( "s - c = 3
\n" ); document.write( "s = (c+3)
\n" ); document.write( "replace s with (c+3) in the 1st equation
\n" ); document.write( "5((c+3) + c) = 32
\n" ); document.write( "5(2c+3) = 32
\n" ); document.write( "10c + 15 = 32
\n" ); document.write( "10c = 32 - 15
\n" ); document.write( "10c = 17
\n" ); document.write( "c = 1.7 mph is the speed of the current
\n" ); document.write( ":
\n" ); document.write( "\"and what was their average speed in still water?\"
\n" ); document.write( "s - 1.7 = 3
\n" ); document.write( "s = 3 + 1.7
\n" ); document.write( "s = 4.7 mph is the speed in still water
\n" ); document.write( ":
\n" ); document.write( ":
\n" ); document.write( "Check this in 2nd original equation
\n" ); document.write( "7(s-c) = 21
\n" ); document.write( "7(4.7-1.7) = 21 \n" ); document.write( "