document.write( "Question 203370: Debbie traveled by boat 5 miles upstream to fish in her favorite spot. Because of the 4-mph current, it took her 20 minuets longer to get there than to return. How fast will her boat go in still water? \n" ); document.write( "
Algebra.Com's Answer #153437 by ankor@dixie-net.com(22740)![]() ![]() You can put this solution on YOUR website! Debbie traveled by boat 5 miles upstream to fish in her favorite spot. \n" ); document.write( " Because of the 4-mph current, it took her 20 minutes longer to get there than to return. \n" ); document.write( "How fast will her boat go in still water? \n" ); document.write( ": \n" ); document.write( "Let s = boat speed in still water \n" ); document.write( "then \n" ); document.write( "(s-4) = speed upstream \n" ); document.write( "and \n" ); document.write( "(s+4) = speed down stream \n" ); document.write( ": \n" ); document.write( "Convert 20 min to hrs: 20/60 = \n" ); document.write( ": \n" ); document.write( "Write a time equation: time = \n" ); document.write( "\n" ); document.write( "Upstream time = downstream time + 20 minutes (1/3 hr) \n" ); document.write( " \n" ); document.write( ": \n" ); document.write( "To clear out these denominators, multiply equation by 3(s+4)(s-4) \n" ); document.write( "3(s+4)(s-4)* \n" ); document.write( "Results in \n" ); document.write( ": \n" ); document.write( "15(s+4) = 15(s-4) + (s+4)(s-4) \n" ); document.write( ": \n" ); document.write( "15s + 60 = 15s - 60 + s^2 - 16 \n" ); document.write( ": \n" ); document.write( "0 = 15s - 15s - 60 - 60 + s^2 - 16 \n" ); document.write( ": \n" ); document.write( "0 = s^2 - 136 \n" ); document.write( ": \n" ); document.write( "s^2 = 136 \n" ); document.write( "s = \n" ); document.write( "s = 11.66 mph speed in still water \n" ); document.write( ": \n" ); document.write( ": \n" ); document.write( "Check solution on calc: (speed up = 7.66 and speed down = 15.66) \n" ); document.write( "5/7.66 - 5/15.66 = .3333 which is 1/3 of an hr\r \n" ); document.write( " \n" ); document.write( " \n" ); document.write( "\n" ); document.write( " \n" ); document.write( " |