26.  A boat covers a certain distance downstream in 1 hour, while it comes back in 1 1/2 hours. if the speed of the stream be 3 km/hr, what is the speed of the boat in still water?


12 km/hr
13 km/hr
14 km/hr
15 km/hr


Answer

 Option

Let the speed of the boat in still water be x km/hr. then, speed downstream = (x+3) km/hr, speed upstream = (x-3) km/hr. Therefore (x+3)*1 = (x-3)*3/2 <=> 2x+6 = 3x-9 <=> x=15km/hr.

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27.  A man can row 9 1/3 km/hr in still water and finds that it takes him thrice as much time to row up than as to row down the same distance in the river. the speed of the current is/


3 1/3 km/hr
3 1/9 km/hr
4 2/3 km/hr
4 1/2 km/hr


Answer

 Option

Let speed upstream be x km/hr.then, speed downstream = 3x km/hr. speed in still water = 1/2 (3x+x) km/hr = 2x km/hr. Therefore 2x =28/3 => x= 14/3. so, speed upstream = 14/3 km/hr ; speed downstream =14 km/hr Hence, speed of the current = 1/2 (14- 14/3) km/hr = 14/3 km/hr =4 2/3 km/hr.

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28.  A boat takes 19 hours for traveling downstream from point A to point B and coming back to a point C midway between A and B. If the velocity of the stream is 4 km/hr and he speed of the boat in still water is 14 km/hr, what is the distance between A and B?


160 km
180 km
200 km
220 km


Answer

 Option

Speed downstream = (14+4) km/hr = 18 km/hr; Speed upstream = (14-4) km/hr = 10 km/hr. Let the distance between A and B be x km. then, x/18+(x-2)/10=19 <=> x/18+x/20 =19 <=> 19x/180 =19 <=> x =180 km.

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29.  A man can row at 5 km/hr in still water. If the velocity of current is 1 km/hr and it takes him 1 hour to row to a place and come back, how far is the place?


2.4km
2.5 km
3 km
3.6 km


Answer

 Option

Speed downstream = (5+1) km/hr = 6 km/hr ; speed upstream = (5-1) km/hr = 4 km/hr. Let the required distance be x km. Then, x/6 + x/4 = 1 <=> 2x+3x =12 <=> 5x =12 <=> x = 2.4 km.

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30.  The speed of a boat in still water is 15 km/hr and the rate of current is 3 km/hr. The distance traveled downstream in 12 minutes is?


1.2 km
1.8 km
2.4 km
3.6 km


Answer

 Option

Speed downstream =(15+3) km/hr = 18 km/hr. distance traveled = (18*12/60) km = 3.6 km.

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