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Boats and Streams:

In water, the direction along the stream is called downstream. And, the direction against the stream is called upstream.

- If the speed of a boat in still water is u km/hr and the speed of the stream is v km/hr, then:

Speed of downstream = (u + v) km/hr

Speed of upstream = (u – v) km/hr - If the speed downstream is a km/hr and the speed upstream is b km/hr, then:

Speed in still water = 1/2 (a + b) km/hr

Rate of stream = 1/2 (a – b) km/hr

# Aptitude Questions:

1. In one hour, a boat goes 11 km along the stream and 5 km against the stream. What is the speed of the boat in still water (in km/hr)?

A) 3

B) 5

C) 8

D) 9

E) None of these

View Answer

Answer: option (C)

Explanation:

Speed in still water = 1/2 (11 + 5) km/hr = 8 km/hr

2. A woman can row upstream at 6 kmph and downstream at 12 kmph. The speed of the stream is:

A) 3 km/hr

B) 4.2 km/hr

C) 5 km/hr

D) 10.5 km/hr

E) None of these

View Answer

Answer: option (A)

Explanation:

Speed of stream = 1/2 (12 – 6) km/hr = 3 km/hr

3. A man rows downstream 32 km and 14 km upstream. If he takes 9 hours to cover each distance, then the velocity (in kmph) of the current is:

A) 1/2

B) 1

C) 1.5

D) 2

E) None of these

View Answer

Answer: option (B)

Explanation:

Rate of downstream = (32/9) kmph; Rate of upstream = (14/9) kmph

∴ Velocity of current = 1/2 (32/9-14/9 ) kmph = 2/2 kmph = 1kmph

4. A boat running downstream covers a distance of 24 km in 2 hours while for covering the same distance upstream, it takes 4 hours. What will be the speed of the boat in still water?

A) 4 km/hr

B) 9 km/hr

C) 8 km/hr

D) 10 km/hr

E) None of these

View Answer

Answer: option (B)

Explanation:

Rate of downstream = (24/2) kmph = 12 kmph; Rate of upstream = (24/4) kmph = 6 kmph

∴ Speed in still water = 1/2 (12 + 6) kmph = 9 kmph

5. A boatman goes 2km against the current of the stream in 1 hour and goes 1 km along the current in 10 minutes. How long will it take to go 5 km in stationery water?

A) 40 minutes

B) 1 hour

C) 1 hr 15 min

D) 1 hr 30 min

E) None of these

View Answer

Answer: option (C)

Explanation:

Rate of downstream = (1/10*60) km/hr = 6 km/hr; Rate of upstream = 2 km/hr

Speed in still water = 1/2 (6 + 2) kmph = 4 kmph

∴ Required time = (5/4) hrs = 1 hr 15 mins