Aptitude - Boats and Streams
Exercise : Boats and Streams - General Questions
- Boats and Streams - Formulas
- Boats and Streams - General Questions
- Boats and Streams - Data Sufficiency 1
- Boats and Streams - Data Sufficiency 2
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?
Answer: Option
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 three-quarters of a kilometre against the stream in 11
minutes and down the stream in 7
minutes. The speed (in km/hr) of the man in still water is:
minutes and down the stream in 7 minutes. The speed (in km/hr) of the man in still water is:Answer: Option
Explanation:
We can write three-quarters 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 |
| = | 25 | m/sec |
| 18 |
| = | |
25 | x | 18 | km/hr |
| 18 | 5 |
= 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:
Answer: Option
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
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 |
| = | 3x | : | 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:
Answer: Option
Explanation:
Suppose he move 4 km downstream in x hours. Then,
| Speed downstream = | |
4 | |
km/hr. |
| x |
| Speed upstream = | |
3 | |
km/hr. |
| x |
|
48 | + | 48 | = 14 or x = | 1 | . |
| (4/x) | (3/x) | 2 |
So, Speed downstream = 8 km/hr, Speed upstream = 6 km/hr.
| Rate of the stream = | 1 | (8 - 6) km/hr = 1 km/hr. |
| 2 |
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