Boats and Streams Shortcuts
- I. Speed of the boat in still water = 1/2 (Downstream speed + Upstream speed)
- II. Downstream speed = Speed of boat in still water + Speed of stream
- III. Upstream speed = Speed of boat in still water – Speed of stream
A boy rows a boat at 12 km/h along the stream and 8 km/h against the stream. Now what is the speed of the boat in still water.
- I. 12km/hr
- II. 10km/hr
- III. 15km/hr
- IV. 8km/hr
Solution-
- Downstream speed of the boat – 12 km/h
- Upstream speed of the boat – 8 km/h
Speed of the boat in still water – ½ (Downstream speed + Upstream speed)
= 1/2 (12 + 8)
= 10 km/h
Correct answer: B
Problem on boat and Stream
Trick- Shortcuts for Boats and Streams
Speed of stream = 1/2 *(Downstream speed – upstream speed)
- I. Speed upstream = (u – v )km/hrs
- II. Speed downstream = (u + v ) km/hr
A boat whose speed in 15 km/hr in still water goes 30 km downstream and it takes 4.5 hrs to come back. What will be the speed of the stream
- I. A . 25km/hr
- II. B. 15m/hr
- III. C. 20km/hr
- IV. D. 5km/hr
Solution:
Let the speed of stream = x
Therefore, speed downstream = 15 + x
Speed upstream = 15 – x
30/(15+x) + 30/(15-x) = 4hr 30 min
30/(15+x)+ 30/(15-x) = 9/2
Finaly
x = 5km/hr