41.  A man rows downstream 32 km and 14 km upstream.If he takes 6 hours to cover each distance then the velocity (in km/ph) of the current is?


1/2
1
1 1/2
2


Answer

 Option

Rate downstream = (32/6)km/ph; Rate upstream = (14/6) km/ph Velocity of current = 1/2 (32/6 - 14/6) km/ph = 3/2 km/ph = 1.5 km/ph

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42.  A man can row upstream at 8km/ph and downstream at 13 km/ph.The speed of the stream is?


2.5 km/hr
4.2 km/hr
5 km/hr
10.5 km/hr


Answer

 Option

Speed of stream = 1/2(13 - 8)km/ph = 2.5 km/ph

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


3
5
8
9


Answer

 Option

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

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44.  A man can row 40 km upstream and 55 km downstream in 13 hours. Also, he can row 30 km upstream and 44 km downstream in 10 hours. find the speed of the man in still water and the speed of the current?


3 km/hr
8 km/hr
5 km/hr
10 km/hr


Answer

 Option

Let rate upstream =x km/hr and rate downstream = Y km/hr Then 40/x+55/y = 13........(1) and 30/x+44/y = 10 Multiplying (2) by 4 and (1) by 3 and subtracting, we get 11/y =1 substituting y = 11 in (1) we get : x=5 Rate in still water = 1/2 (11+5) km/ph = 8 km/ph Rate of current = 1/2 (11-5) km/ph = 3 km/ph

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45.  In a stream running at 2 km/hr. a motorboat goes 6 km upstream and back again to the starting point in 33 minutes. Find the speed of the motorboat in still water?


22 km/hr
30 km/hr
35 km/hr
40 km/hr


Answer

 Option

Let the speed of the motorboat in still water be x km/hr. then, speed downstream = (x+2) km/hr ; speed upstream = (x-2) km/hr. Therefore 6/x+2 + 6/ x-2 = 33/60 <=> 11x^2- 240x-44=0 <=> 11x^2 - 242x+2x - 44 =0 <=> (x-22) (11x+2) =0 <=> x=22. Hence, speed of motorboat in still water = 22 km/hr.

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