document.write( "Question 637732: A boat traveled 252 miles downstream and back. the trip downstream took 14 hours. the trip back took 21 hours. what is the speed of the boat in still water? what is the speed of the current? \n" ); document.write( "
Algebra.Com's Answer #401845 by DrBeeee(684)\"\" \"About 
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Use the formula d = rt.
\n" ); document.write( "Where d is the distance travelled (miles)
\n" ); document.write( "r is the rate of travel (miles/hour)
\n" ); document.write( "t is the time of travel (hours)
\n" ); document.write( "Downstream your rate is the speed of the boat (b) PLUS the speed of the current (c) for a net speed of (b+c). Upstream the current is \"working\" against the boat so the net speed is (b-c).
\n" ); document.write( "Downstream equation
\n" ); document.write( "d = (b+c)*t, applying the given values for the downstream trip yields
\n" ); document.write( "(1) 252 = (b+c)*14
\n" ); document.write( "Upstream equation
\n" ); document.write( "d = (b-c)*t, applying the given values for the upstream trip yields
\n" ); document.write( "(2) 252 = (b-c)*21
\n" ); document.write( "Now solve (1) and (2) simultaneously
\n" ); document.write( "(1) b+c = 252/14 = 18
\n" ); document.write( "(2) b-c = 252/21 = 12
\n" ); document.write( "Add (1) and (2)
\n" ); document.write( "(b+c)+(b-c) = 18 + 12
\n" ); document.write( "2b +0 = 30
\n" ); document.write( "b = 15
\n" ); document.write( "(1) 15 + c = 18
\n" ); document.write( "c = 3
\n" ); document.write( "Correct? Let's check.
\n" ); document.write( "Is (252=(15+3)*14)?
\n" ); document.write( "Is (252=18*14)?
\n" ); document.write( "Is (252=252)? Yes
\n" ); document.write( "Is (252=(15-3)*21)?
\n" ); document.write( "Is (252=12*21)?
\n" ); document.write( "Is (252=252)? Yes
\n" ); document.write( "Answer: The speed of the boat in still water is 15 mph and the speed of the current is 3 mph \n" ); document.write( "
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