Question 620130
  <pre><font face = "Tohoma" size = 3 color = "indigo"><b> 
Hi
A canoe takes 7 hours to travel 48 km down a river and back.The rate of the current of the river is 2 kmph.
Find the rate{{{highlight(r)}}}of the canoe in still(calm) water.
 D =rt   or  D/r = t
  {{{48/(r+2)   +48/(r-2) = 7hr}}}   |Multiplying thru by (r+2)(r-2)so as all denominators = 1
   48(r-2) + 48(r+2) = 7(r+2)(r-2)
         96r = 7(r^2 - 4)
            7r^2 - 96r - 28 = 0  
             (7r+2)(r - 14) = 0  |throwing out negative solution for rate
                       r = 14 kmph is the speed of the canoe in still(calm) water.
CHECKING our Answer***
   {{{ 48km/16kmph +48km/12kmph}}} = 3hr + 4hr = 7hr