Boats And Streams

What is the speed of the boat in still water?
I.	The speed downstream is 12 kmph.
II.	The speed upstream is 4 kmph.
III.	In a to and fro journey between two points, the average speed of the boat was 6 kmph.

A:

I and II only

B:

All I, II and III

C:

III, and either I or II

D:

Any two of the three

Answer: D

From I and II, speed of boat in still water =	1	(12 + 4) km/hr = 8 km/hr.
	2

From II and III, we get:

Using average speed =	2xy	, we get:	2 x 4 x y	= 6
	x + y		4 + y

8y = 24 + 6y

y = 12.

Required speed =	1	(12 + 4) km/hr = 8 km/hr.
	2

Similarly, I and III also give the answer.

Correct answer is (D).

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What is the speed of the boat in still water?
I.	The boat covers a distance of 48 kms in 6 hours while running upstream.
II.	The boat covers the same distance in 4 hours while running downstream.

A:

I alone sufficient while II alone not sufficient to answer

B:

II alone sufficient while I alone not sufficient to answer

C:

Either I or II alone sufficient to answer

D:

Both I and II are not sufficient to answer

Answer: E

I. Speed upstream =	48	km/hr = 8 km/hr.
	6

II. Speed downstream =	48	km/hr = 12 km/hr.
	4

Speed of the boat =	1	(8 + 12) km/hr = 10 km/hr.
	2

Thus, I and II together give the answer.

Correct answer is (E).

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What is the speed of the boat in still water?
I.	It takes 2 hours to cover the distance between A and B downstream.
II.	It takes 4 hours to cover the distance between A and B upstream.

A:

I alone sufficient while II alone not sufficient to answer

B:

II alone sufficient while I alone not sufficient to answer

C:

Either I or II alone sufficient to answer

D:

Both I and II are not sufficient to answer

Answer: D

Let AB = x km.

I. Speed downstream =	x	km/hr
	2

II. Speed upstream =	x	km/hr.
	4

Speed of boat in still water =	1		x	+	x	km/hr.
	2		2		4

Thus, I and II both even do not give the answer.

Correct answer is (D).

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A boat takes a total time of three hours to travel downstream from P and Q and upstream back from Q to P. What is the speed of the boat in still water?
I.	The speed of the river current is 1 km per hour.
II.	The distance between P and Q is 4 km.

A:

I alone sufficient while II alone not sufficient to answer

B:

II alone sufficient while I alone not sufficient to answer

C:

Either I or II alone sufficient to answer

D:

Both I and II are not sufficient to answer

Answer: E

I. Speed of the current = 1 km/hr.

II. PQ = 4 km.

Let the speed of the boat in still water be x km/hr. Then,

4	+	4	= 3. This gives x.
(x + 1)		(x - 1)

Correct answer is (E).

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A man rows to a place 48 km distant and come back in 14 hours. He finds that he can row 4 km with the stream in the same time as 3 km against the stream. The rate of the stream is:

A:

1 km/hr

B:

1.5 km/hr

C:

2 km/hr

D:

2.5 km/hr

Answer: A

Suppose he move 4 km downstream in x hours. Then,

Speed downstream =		4		km/hr.
		x

Speed upstream =		3		km/hr.
		x

	48	+	48	= 14 or x =	1	.
	(4/x)		(3/x)		2

So, Speed downstream = 8 km/hr, Speed upstream = 6 km/hr.

Rate of the stream =	1	(8 - 6) km/hr = 1 km/hr.
	2

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Questions for: Boats And Streams