You can paddle your canoe seven miles per hour through any placid lake. The stream flows at three miles per hour. The moment you start to paddle up stream a fisherman looses one of his bobbers in the water fourteen miles up stream of you.
How many hours does it take for you and the bobber to meet?

• the speed of the canoe in still waters = 7 MPH
  the speed of the stream = 3 MPH
  relative speed of the canoe upstream= 7 - 3 = 4 MPH
  the distance between the fishing hobber and the canoe = 14 MPH
  let the hobber and the canoe meet at a distance D from the starting point of canoe.
  then the distance of the meeting point from the fisherman is = 14 - D
  using the formula D = ST, we have
  for the canoe, D= 4T, for the bobber, 14 - D = 3T ( speed of bobber = speed of strem= 3 MPH)
  T is same in both equations, hence D/4 = (14 - D)/3
  3D = 4 (14 - D)
  3D = 56 - 4D
  7D = 56
  or D = 8 miles
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