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Boats and Streams ( 21 to 25 ):

# APTITUDE QUESTIONS (BOATS AND STREAMS):

21. A boat covers 24 km upstream and 36 km downstream in 6 hours while it covers 36 km upstream and 24 km downstream in 6(1/2) hours. The velocity of the current is:

A) 1 km/hr

B) 1.5 km/hr

C) 2 km/hr

D) 2.5 km/hr

E) None of these

View Answer

Answer: option (C)

Explanation:

Let rate upstream = x kmph and rate downstream = y kmph

Then, 24/x + 36/y = 36 …(i) and 36/x + 24/y = 13/2 …(ii)

Adding (i) and (ii), we get: 60(1/x+1/y) = 25/2 or 1/x+1/y = 5/24 …(iii)

Subtracting (i) from (ii), we get: 12(1/x-1/y) = 1/2 or 1/x-1/y = 1/24 …(iv)

Adding (iii) and (iv), we get: 2/x = 6/24 or x = 8

So, 1/8 + 1/y = 5/24 1/y = (5/24-1/8) = 1/12 y = 12

∴ Speed upstream = 8 kmph, Speed downstream = 12 kmph

Hence, rate of current = 1/2(12 – 8) kmph = 2 kmph

22. A woman can row upstream at 8 kmph and downstream at 10 kmph. Find woman’s rate in still water and the rate of current.

A) 7, 1.5 km/hr

B) 9, 1 km/hr

C) 8, 2 km/hr

D) 7.5, 2.5 km/hr

E) None of these

View Answer

Answer: option (B)

Explanation:

Rate in still water = 1/2(10 + 8) kmph = 9 km/hr

Rate of current = 1/2(10 – 8) kmph = 1 km/hr

23. A man takes 3 hours to row a boat 15 km downstream of a river and 2 hours to cover a distance of 6 km upstream. Find the speed of the river current in km/hr.

A) 2 km/hr

B) 3 km/hr

C) 1 km/hr

D) 4 km/hr

E) None of these

View Answer

Answer: option (C)

Explanation:: Answer is C

Rate downstream = (15/3) km/hr = 5 km/hr

Rate upstream = (6/2) km/hr = 3 km/hr

∴ Speed of current = 1/2(5 – 3) kmph = 1 km/hr

24. A boat running downstream covers a distance of 14 km in 2 hours while for covering the same distance upstream, it takes 7 hours. What is the speed of the boat in still water?

A) 4.5 km/hr

B) 6.5 km/hr

C) 8.5 km/hr

D) 5.5 km/hr

E) None of these

View Answer

Answer: option (A)

Explanation:

Rate downstream = (14/2) km/hr = 7 km/hr

Rate upstream = (14/7) km/hr = 2 km/hr

∴ Speed in still water = 1/2(7 + 2) km/hr = 4.5 km/hr

25. The speed of a boat in still water is 12 km/hr and the rate of current is 4 km/hr. The distance travelled downstream in 15 minutes is:

A) 2 km

B) 3 km

C) 5 km

D) 4 km

E) None of these

View Answer

Answer: option (D)

Explanation:

Speed downstream = (12 + 4) km/hr = 16 km/hr

Distance travelled = (16*15/60) = 4 km