Quick Review: Boats and Streams

Boats & Streams is one of the favorite areas of examiners. Questions from this area appear in a significant proportion in the quant section of almost all the competitive exams. Before starting with the questions, go through the basic concepts of the topic.
Pml Web Banner
Important Terms
  • Still Water: If the speed of the water is zero, i.e. water is stationary, then it is called still water.
  • Stream: The moving water in the river is known as a stream.
  • Upstream: If a boat or a swimmer moves in the opposite direction of the stream, then it is called upstream.
  • Downstream: If a boar or a swimmer moves in the same direction of the stream, then it is called downstream.
  • When the speed of a boat or a swimmer is given, it usually means speed in still water.
Formulae
Suppose the speed of boat in still water is u km/hr and the speed of the stream is v km/hr.
Then:
  • Upstream Speed: It is the speed of the boat against the stream = (u - v) km/hr
  • Downstream Speed: It is the speed of the boat with the stream = (u + v) km/hr
  • If upstream is denoted as US and downstream as DS, then:
    Speed of boat or swimmer in still water = 1/2 (Ds + Us)
    Speed of stream =1/2 (Ds - Us)
  • If a man is capable of rowing at the speed of u km/hr in still water, rows the equal distance up and down the stream which flows at a rate of v km/hr, then the average speed throughout the journey
  • A man can row a boat in still water at u km/hr. A stream is flowing at v km/hr and it take t hrs more in upstream than to go downstream for the same distance, then the distance is calculated by = (u2 – v2)t/2v km
  • A man rows a certain distance downstream in t1 hrs and returns the same distance upstream in t2 hrs. If the speed of the stream is v km/hr, then the speed of the man in still water will be calculated by
  • A man can row a boat in still water at u km/hr. In a stream flowing at v km/hr if it takes him t hrs to row to a place and come back, then the distance between the two places is
  • A boat or a swimmer takes n times as long as to row upstream as to row downstream the river. If the speed of the boat or the swimmer is u km/hr in still water and speed of stream is v km/hr, then
bimtech