Answer to Question #6721 in Differential Equations for cormac

Question

1.A woman is on a lake in a canoe 1km from the closest point P of a straight shoreline. She wants to get to a point Q, 10km along the shore from P. To do so, she paddles to a point R between P and Q and then walks the remaining distance to Q. She can paddle 3km/hour and walk 5km/hour. How should she pick the point R so that she gets to Q as quickly as possible?