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?

A. 12 km/hr B. 13 km/hr C. 14 km/hr D. 15 km/hr

Answer Answer: Option D Explanation: 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.

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/

A. 3 1/3 km/hr B. 3 1/9 km/hr C. 4 2/3 km/hr D. 4 1/2 km/hr

Answer Answer: Option C Explanation: 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.

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?

A. 160 km B. 180 km C. 200 km D. 220 km

Answer Answer: Option B Explanation: 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.

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?

A. 2.4km B. 2.5 km C. 3 km D. 3.6 km

Answer Answer: Option A Explanation: 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.