The boats and streams problems are based on the concepts of time, speed, and distance. However, a few adjustments need to be made in case of such problems.
Boats and streams is one of the most common topics of all the job entrance exams.It is also included in Aptitude section of many job test in companies like TCS, Infosys etc. This a very simple topic and require to direct application of Formulas to solve the question.
Speed of the boat in still water = 1/2 (Downstream speed + Upstream speed)
Downstream speed = Speed of boat in still water + Speed of stream
Upstream speed = Speed of boat in still water – Speed of stream
Question 1:A man rows a boat at 12 km/h along the stream and 8 km/h against the stream. Find the speed of the boat in still water.
Options:
A. 12km/hr
B. 10km/hr
C. 15km/hr
D. 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 = 1/2*(Downstream speed + Upstream speed)
= 1/2 (12 + 8)
= 10 km/h
Correct option: B
Speed of stream = 1/2 *(Downstream speed – upstream speed)
Speed downstream = (u + v ) km/hr.
Speed upstream = (u – v ) km/hr.
Question 1:A boat whose speed in 15 km/hr in still water goes 30 km downstream and it takes 4 hours 30 minutes to come back. Find the speed of the stream?
Options:
A . 25km/hr
B. 15m/hr
C. 20km/hr
D. 5km/hr
Solution: Let the speed of the 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
On solving we get
x = 5km/hr
Correct option: D
Question 1:A sailor can row 6 km/h in still water. It takes him twice as long to row up as to row down the river. Find the speed of the stream.
Options:
A. 6 km/ hr
B. 5 km/ hr
C. 3 km/ hr
D. 2 km/ hr
Solution: Let sailor’s speed in upstream = x
Downstream speed = 2x (As given in the question, his downstream speed is twice of upstream speed)
Man’s speed in still water = 1/2 (Upstream speed + Downstream speed)
= 1/2 (x + 2x) = 3x/2
3x/2 = 6 (sailor can row 6 km/h in still water)
x = 4 km/hr
Therefore, upstream speed = x = 4 km/hr
Downstream speed = 2x = 2 * 4 = 8 km/hr
Speed of stream = 1/2* (Downstream speed – Upstream speed)
= 1/2 (8 – 4)
= 2 km/ hr
Correct option: D