Aptitude - Boats and Streams - Discussion
Discussion Forum : Boats and Streams - General Questions (Q.No. 11)
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 |
Discussion:
28 comments Page 3 of 3.
Sonia said:
8 years ago
1hr = 60mins.
So, 1/4 of 1 hr = 1/4*60= 15min.
So, 1/4 of 1 hr = 1/4*60= 15min.
MohitRaj said:
1 decade ago
We know that,
Upstream speed = u-v;
Downstream speed=u+v;.
According to formula, s=d/t.
u-v = 2/1, and
u+v = 60/10.
On solving these equations, we get.
u=4 and v=2.
Therefore, speed of boatman = 4 km/hr.
Hence, t=d/s.
t=5/4.
We get 1hr 15min is answer.
Upstream speed = u-v;
Downstream speed=u+v;.
According to formula, s=d/t.
u-v = 2/1, and
u+v = 60/10.
On solving these equations, we get.
u=4 and v=2.
Therefore, speed of boatman = 4 km/hr.
Hence, t=d/s.
t=5/4.
We get 1hr 15min is answer.
Rajesh Rapelly said:
9 years ago
Let Speed of the boat is 'u' and Speed of the Stream is 'v'.
Then u+v=6km/hr ///Speed of the boat in downstream.
Then u-v=2km/hr ////Speed of the boat in upstream.
Here we need the speed of the boat in Still Water which is 'u', because the speed of stream is zero in still water i.e;v=0.
By solving u+v =6 & u-v=2 ,we get u=4km/hr.
Ao, Speed of the boat in Stillwater is 4km/hr, then to travel 5km it take 1hr 15mins.
Then u+v=6km/hr ///Speed of the boat in downstream.
Then u-v=2km/hr ////Speed of the boat in upstream.
Here we need the speed of the boat in Still Water which is 'u', because the speed of stream is zero in still water i.e;v=0.
By solving u+v =6 & u-v=2 ,we get u=4km/hr.
Ao, Speed of the boat in Stillwater is 4km/hr, then to travel 5km it take 1hr 15mins.
Kas said:
1 decade ago
How to calculate the required time ?
Darth vadar said:
1 decade ago
Divide 5 by 4 we get 0.25. So why the answer is 1 hr 15 min instead of 1 hr 25 min.
Anu said:
1 decade ago
How can rate upstream be 2 km/hr?
Sowmya said:
1 decade ago
I can't understand, please help me.
Lohith said:
1 decade ago
s = d/t;
u-v = 2/1;
u-v = 2.
u+v = 2/10/60.
u+v = 12.
u = 7.
v = 5.
Final value = 5/7 which is less than a hour.
u-v = 2/1;
u-v = 2.
u+v = 2/10/60.
u+v = 12.
u = 7.
v = 5.
Final value = 5/7 which is less than a hour.
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