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A man rows a boat 910 feet upstream against a constant current in 14 minutes.
\n" ); document.write( " He then rows 525 feet downstream (with the same current) in 7 minutes.
\n" ); document.write( " Find the speed of the current and the equivalent rate at which he can row in still water.
\n" ); document.write( ":
\n" ); document.write( "let s = rowing speed in still water in ft/min
\n" ); document.write( "let c = rate of the current
\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 way. Dist = speed * time
\n" ); document.write( ":
\n" ); document.write( "14(s-c) = 910
\n" ); document.write( " 7(s+c) = 525
\n" ); document.write( "We can greatly simplify these equations, divide the 1st by 17, the 2nd by 7
\n" ); document.write( "then use elimination
\n" ); document.write( "s - c = 65
\n" ); document.write( "s + c = 75
\n" ); document.write( "-------------Addition eliminates c find s
\n" ); document.write( "2s = 140
\n" ); document.write( "s = 140/2
\n" ); document.write( "s = 70 ft/min the speed in still water
\n" ); document.write( ":
\n" ); document.write( "Find the current using s + c = 75
\n" ); document.write( "70 + c = 75
\n" ); document.write( "c = 75 - 70
\n" ); document.write( "c = 5 ft/min the rate of the current
\n" ); document.write( ":
\n" ); document.write( ":
\n" ); document.write( "Confirm this in the 1st original equation
\n" ); document.write( "14(70 - 5) = 910
\n" ); document.write( "14(65) = 910\r
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