1.  A man can row upstream 10 km/ph and downstream 20 km/ph. Find the man rate in still water and rate of the stream.


0,5
5,5
15,5
10,5


Answer

 Option

Rate in still water = 1/2(20+10) = 15 km/ph Rate of current = 1/2(20-10) = 5 km/ph

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2.  A man takes 3 hours 45 minutes to row a boat 15 km downstream of a river and 2 hours 30 minutes to cover a distance of 5 km upstream.Find the speed of the river current in km/hr?


0.5 km/hr
1 km/hr
2 km/hr
2.5 km/hr


Answer

 Option

Rate downstream = (15/3 3/4)km/hr = (15*4/15) = 4 km/hr Rate upstream = (5/2 1/2) km/hr = (5*2/5) km/hr = 2km/hr Speed of current = 1/2 ( 4-2) km/hr = 1 km/hr

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3.  Two persons A and B start from the opposite ends of a 450 km straight truck and run to and from between the two ends. The speed of the first person is 25 m/s and the speed of other is 35 m/s. They continue their motion for 10 hours. How many times did they pass each other?


1
4
3
2


Answer

 Option

First person speed = 25m/s *18/5 = 90 kmph. Second person speed = 35m/s *18/5 = 126 kmph. First person covers 90*10 = 900 km 900/450 = 2

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4.  At his usual rowing rate, A can travel 12 miles downstream in a certain river in 6 hours less than it takes him to travel the same distance upstream. But if he could double his usual rowing rate for his 24 -mile round trip, the downstream 12 miles would then take only one hour less than the upstream 12 miles. what is the speed of the current in miles per hour?


1 1/3
1 2/3
2 1/3
2 2/3


Answer

 Option

Let the speed still in water be x mph and the speed of the current be y mph. Speed upstream = (x-y): Speed downstream = (x+y) 12/(x-y) -12/(x+y) = 6 <=> 6(x^2 - y^2 = 24y ,<=> x^2-y^2 = 4y <=> x^2 = (4y+y^2)........(1) And 12/(2x-y) - 12/ (2x+y) = 1 <=> 4x^2 - y^2 = 24y <=> x^2 = 24y+y^2/4 .........(2)

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5.  A man rows to a place 48 km distant and 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?


1 km/hr
1.5 km/hr
1.8 km/hr
3.5 km/hr


Answer

 Option

Suppose he moves 4 km downstream in x hours. then, speed downstream = (4/x) km/hr, speed upstream =(3/x) km/hr. Therefore 48/(4/x) + 48/(3/x) =14 so speed downstream = 8 km/hr, speed upstream = 6 km/hr. Rate of the stream = 1/2 (8-6) km/hr = 1 km/hr.

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