# Boat And Stream

29 April 2020

If you are preparing for Quantitative Aptitude, Concepts based on Boat and stream are to be studied and understood well. Lets learn and understand concepts of Boat and Stream.

##### Formulas For Boat and Stream

Downstream / Upstream :  In Water, the direction along the stream is called Downstream. And the direction against the stream is called Upstream.

If the speed of boat in still water is u km/hr & the speed of stream is v km/hr, then,

Speed Downstream: (u + v) km/hr

Speed Upstream: (u - v) km/hr

If the Speed Downstream is a km/hr & the Speed Upstream is b km/hr , then:

Speed in still water = (a + b) / 2 km/hr

Rate of stream = (a - b) /2 km/hr

##### Practice Questions For Boat And Stream

Q1) A man's speed with the current is 15 km/hr and the speed of the current is 2.5 km/hr. The man's speed against the current is:

A) 9 km/hr

B) 12.5 km/hr

C) 8.5 km/hr

D) 10 km/hr.

Solution :

Q2) A motorboat, whose speed in 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream (in km/hr) is:

A) 5

B) 4

C) 6

D) 10

Solution :

Q3) In one hour, a boat goes 14 km/hr along the stream and 8 km/hr against the stream. The speed of the boat in still water (in km/hr) is:

A) 8 km/hr

B) 11 km/hr

C) 12 km/hr

D) 10 km/hr

Solution :

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Q4) A boatman goes 2 km against the current of the stream in 2 hour and goes 1 km along the current in 20 minutes. How long will it take to go 5 km in stationary water?

A) 4 hr

B) 2 hr 30 min

C) 2 hr

D) 1 hr 15 min

Solution :

Q5) A boat can travel with a speed of 13 km/hr in still water. If the speed of the stream is 4 km/hr, find the time taken by the boat to go 68 km downstream.

A) 2 hours

B) 3 hours

C) 4 hours

D) 5 hours

Solution:

Speed downstream = (13 + 4) km/hr = 17 km/hr.
Time taken to travel 68 km downstream =68/17hrs = 4 hrs.

Q6) A man can row upstream 10 kmph and downstream 20 kmph. Find the man rate in still water and rate of the stream.

A) 0,5

B) 5,5

C) 15,5

D) 10,5

Solution:

If a is rate downstream and b is rate upstream
Rate in still water = 1/2(a+b)
Rate of current = 1/2(a-b)
=> Rate in still water = 1/2(20+10) = 15 kmph
=> Rate of current = 1/2(20-10) = 5 kmph

Q7) A man's speed with the current is 15 km/hr and the speed of the current is 2.5 km/hr. The man's speed against the current is:

A) 8.5 km/hr
B) 10 km/hr
C) 12.5 km/hr
D) 9 km/hr

Solution:

Man's speed with the current = 15 km/hr
=> speed of the man + speed of the current = 15 km/hr
speed of the current is 2.5 km/hr
Hence, speed of the man = 15 - 2.5 = 12.5 km/hr
man's speed against the current = speed of the man - speed of the current
= 12.5 - 2.5 = 10 km/hr

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Q8) A man takes 20 minutes to row 12 km upstream which is a third more than the time he takes on his way downstream. What is his speed in still water?

A) 41 km/hr
B) 36 km/hr
C) 42 km/hr
D) 45 km/hr

Solution:

Let the speed in still water = x km/hr. Takes 20 min. to row 12 km upstream ? speed of u/s = 36
km/hr. Also, time taken for u/s is 1/3 more than for d/s.
distance covered in d / s will be 1/3 more.
Hence distance covered by man for d / s in 20 min. = 12 × (12/3) = 16km.
So speed of d / s = 48 km/hr.
x + y = 48 and x – y = 36 ? x = 42 km/hr.

Q9) A man's speed with the current is 15 km/hr and the speed of the current is 2.5 km/hr. The man's speed against the current is:

A) 8.5 km/hr
B) 10 km/hr
C) 12.5 km/hr
D) 9 km/hr

Solution:

Man's speed with the current = 15 km/hr
=> speed of the man + speed of the current = 15 km/hr
speed of the current is 2.5 km/hr.
Hence, speed of the man = 15 - 2.5 = 12.5 km/hr
man's speed against the current = speed of the man - speed of the current = 12.5 - 2.5 = 10 km/hr

Q10) In one hour, a boat goes 11km along the stream and 5 km against it. Find the speed of the boat in still water

A) 6

B) 7

C) 8

D) 9

Solution:

We know we can calculate it by 1/2(a+b)=> 1/2(11+5) = 1/2(16) = 8 km/hr.

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