document.write( "Question 442300: A boat traveled 210 miles downstream and back. The trip downstream took 10 hours. The trip back
\n" ); document.write( "took 70 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 #853300 by ikleyn(53479) $\"\"$ $\"About$

You can put this solution on YOUR website!
.
\n" ); document.write( "A boat traveled 210 miles downstream and back. The trip downstream took 10 hours. The trip back
\n" ); document.write( "took 70 hours. What is the speed of the boat in still water? What is the speed of the current?
\n" ); document.write( "~~~~~~~~~~~~~~~~~~~~~~~~~\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "        The solution by @mananth has too much excessive calculations,\r
\n" ); document.write( "\n" ); document.write( "        which means that his computer code, which produces his text and calculations,\r
\n" ); document.write( "\n" ); document.write( "        is badly organized and creates anti-pedagigic narrative.\r
\n" ); document.write( "\n" ); document.write( "        As a result, the solution by @mananth scares readers and is a bad way to teach.\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "        Below is my solution, which is a standard treatment of the problem without making unnecessary calculations.\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "

\r\n" );
document.write( "The effective speed downstream is\r\n" );
document.write( "\r\n" );
document.write( "     = 21 mph.\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "The effective speed upstream is\r\n" );
document.write( "\r\n" );
document.write( "     = 3 mph.\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "If u  is the rate of the boat at no current and v is the rate of current, then\r\n" );
document.write( "\r\n" );
document.write( "    u + v = 21    (1)\r\n" );
document.write( "\r\n" );
document.write( "    u - v =  3    (2)\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "By adding equations, you get  2u = 21 + 3 = 24,  u = 24/2 = 12 mph.\r\n" );
document.write( "\r\n" );
document.write( "Bu subtracting eq.(2) from eq.(1), you get  2v = 21 - 3 = 18,  v = 18/2 = 9 mph.\r\n" );
document.write( "\r\n" );
document.write( "\r\n" );
document.write( "ANSWER.  The rate of the boat at no current is 12 mph.\r\n" );
document.write( "\r\n" );
document.write( "         The rate of the current is 9 mph.\r\n" );
document.write( "

\r
\n" ); document.write( "\n" ); document.write( "Solved in the most straightforward form and in the most educative way, without making excessive calculations.\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( " \n" ); document.write( "

\n" );