Answer: Option C
Explanation:
Speed in still water =  1  (11 + 5) kmph = 8 kmph. 
2 
6. 
A boat running downstream covers a distance of 16 km in 2 hours while for covering the same distance upstream, it takes 4 hours. What is the speed of the boat in still water?

A.  4 km/hr 
B.  6 km/hr 
C.  8 km/hr 
D.  Data inadequate 
Answer: Option B
Explanation:
Rate downstream = 
 16  kmph = 8 kmph. 
2 
Rate upstream = 
 16  kmph = 4 kmph. 
4 
Speed in still water =  1  (8 + 4) kmph = 6 kmph. 
2 

7. 
The speed of a boat in still water in 15 km/hr and the rate of current is 3 km/hr. The distance travelled downstream in 12 minutes is:

Answer: Option D
Explanation:
Speed downstream = (15 + 3) kmph = 18 kmph.
Distance travelled =   18 x  12  km = 3.6 km. 
60 

8. 
A boat takes 90 minutes less to travel 36 miles downstream than to travel the same distance upstream. If the speed of the boat in still water is 10 mph, the speed of the stream is:

Answer: Option A
Explanation:
Let the speed of the stream x mph. Then,
Speed downstream = (10 + x) mph,
Speed upstream = (10  x) mph.
 36    36  =  90 
(10  x)  (10 + x)  60 
72x x 60 = 90 (100  x^{2})
x^{2} + 48x  100 = 0
(x+ 50)(x  2) = 0
x = 2 mph.

9. 
A man can row at 5 kmph in still water. If the velocity of current is 1 kmph and it takes him 1 hour to row to a place and come back, how far is the place?

Answer: Option A
Explanation:
Speed downstream = (5 + 1) kmph = 6 kmph.
Speed upstream = (5  1) kmph = 4 kmph.
Let the required distance be x km.
2x + 3x = 12
5x = 12
x = 2.4 km.

10. 
A boat covers a certain distance downstream in 1 hour, while it comes back in 1 hours. If the speed of the stream be 3 kmph, what is the speed of the boat in still water?

A.  12 kmph 
B.  13 kmph 
C.  14 kmph 
D.  15 kmph 
E.  None of these 
Answer: Option D
Explanation:
Let the speed of the boat in still water be x kmph. Then,
Speed downstream = (x + 3) kmph,
Speed upstream = (x  3) kmph.
(x + 3) x 1 = (x  3) x  3 
2 
2x + 6 = 3x  9
x = 15 kmph.
11. 
A boatman goes 2 km against the current of the stream in 1 hour and goes 1 km along the current in 10 minutes. How long will it take to go 5 km in stationary water?

A.  40 minutes 
B.  1 hour 
C.  1 hr 15 min 
D.  1 hr 30 min 
Answer: Option C
Explanation:
Rate downstream = 
 1  x 60  km/hr = 6 km/hr. 
10 
Rate upstream = 2 km/hr.
Speed in still water =  1  (6 + 2) km/hr = 4 km/hr. 
2 
Required time = 
 5  hrs = 1  1  hrs = 1 hr 15 min. 
4  4 

12. 
A man can row threequarters of a kilometre against the stream in 11 minutes and down the stream in 7minutes. The speed (in km/hr) of the man in still water is:

Answer: Option D
Explanation:
We can write threequarters of a kilometre as 750 metres,
and 11 minutes as 675 seconds.
Rate upstream =   750  m/sec  =  10  m/sec. 
675  9 
Rate downstream = 
 750  m/sec  =  5  m/sec. 
450  3 
Rate in still water =  1  (  10  +  5  )m/sec 
2  9  3 
= 5 km/hr.

13. 
Speed of a boat in standing water is 9 kmph and the speed of the stream is 1.5 kmph. A man rows to a place at a distance of 105 km and comes back to the starting point. The total time taken by him is:

A.  16 hours 
B.  18 hours 
C.  20 hours 
D.  24 hours 
Answer: Option D
Explanation:
Speed upstream = 7.5 kmph.
Speed downstream = 10.5 kmph.
Total time taken =   105  +  105  hours = 24 hours. 
7.5  10.5 

14. 
A man takes twice as long to row a distance against the stream as to row the same distance in favour of the stream. The ratio of the speed of the boat (in still water) and the stream is:

Answer: Option B
Explanation:
Let man's rate upstream be x kmph.
Then, his rate downstream = 2x kmph.
(Speed in still water) : (Speed of stream) =   2x + x   :   2x  x  
2  2 
= 3 : 1.

15. 
A man rows to a place 48 km distant and come 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:

A.  1 km/hr 
B.  1.5 km/hr 
C.  2 km/hr 
D.  2.5 km/hr 
Answer: Option A
Explanation:



No comments:
Post a Comment