Aptitude - Boats and Streams - Discussion
Discussion Forum : Boats and Streams - General Questions (Q.No. 4)
4.
A motorboat, whose speed in 15 km/hr in still water goes 30 km downstream and comes back in a total of 4 hours 30 minutes. The speed of the stream (in km/hr) is:
Answer: Option
Explanation:
Let the speed of the stream be x km/hr. Then,
Speed downstream = (15 + x) km/hr,
Speed upstream = (15 - x) km/hr.
 |
30 | + | 30 | = 4 | 1 |
| (15 + x) | (15 - x) | 2 |
 |
900 | = | 9 |
| 225 - x2 | 2 |
9x2 = 225
x2 = 25
x = 5 km/hr.
Video Explanation: https://youtu.be/lMFnNB3YQOo
Discussion:
63 comments Page 3 of 7.
Saji said:
3 years ago
(30/15+x) + (30/15-x) =4 (1/2).
By cross multiplying;
(30(15-x) + 30(15+x)) /(15+x) (15-x) = 9/2.
(450-30x+450+30x)/15^2 - x^2 = 9/2.
-30x and +30x get cancelled.
So,
900/15^2 -x^2 = 9/2.
By cross multiplying;
(30(15-x) + 30(15+x)) /(15+x) (15-x) = 9/2.
(450-30x+450+30x)/15^2 - x^2 = 9/2.
-30x and +30x get cancelled.
So,
900/15^2 -x^2 = 9/2.
(5)
P Dixit said:
9 years ago
Put in Formula.
If total Distance = D= 30, Total Time = T= 9/2 Hr., Boat Speed= B = 30, Stream Speed = S=?,
Then,
Distance between the two places is D = T(B^2 - S^2)/2B
S = 5 Ans.
If total Distance = D= 30, Total Time = T= 9/2 Hr., Boat Speed= B = 30, Stream Speed = S=?,
Then,
Distance between the two places is D = T(B^2 - S^2)/2B
S = 5 Ans.
Sagar said:
1 decade ago
In a stream running at 2km/h, a motor boat goes 10 km upstream and back again to the starting point in 55 minutes. Find the speed of the motorboat in still water? Please answer.
Pawan thakur said:
8 years ago
Sneha just like that 4 hours 30 minutes.
Convert 30 minutes 30/60 you will get 1/2.
Now 4 hours 30 minutes = 4*1/2 you will get 9/2 in place of 30 minutes put 1/2.
Convert 30 minutes 30/60 you will get 1/2.
Now 4 hours 30 minutes = 4*1/2 you will get 9/2 in place of 30 minutes put 1/2.
Varun said:
1 decade ago
Here only one direction distance is given. Time which requires to go and back position is given. How is possible to put total time to only one direction distance.
Ajax said:
1 decade ago
Simple to find speed of stream to check option.
A) 4.
= 15+4/2 + 15-4/2.
= 4.25 hr so wrong.
B) 5.
= 15+5/2 + 15-5/2.
= 4.5 hr so right answer.
A) 4.
= 15+4/2 + 15-4/2.
= 4.25 hr so wrong.
B) 5.
= 15+5/2 + 15-5/2.
= 4.5 hr so right answer.
Mohanraj said:
1 decade ago
Friends this step is little confused any can help please?
(30/(15+v))+(30/(15-v)) = 4 1/2.
(30*30/(15-v)(15+v)) = 4 1/2.
(30/(15+v))+(30/(15-v)) = 4 1/2.
(30*30/(15-v)(15+v)) = 4 1/2.
Krishna said:
8 years ago
The answer is 4 * 1/2 = 2.
How is it possible the answer is 9/2. If 4+1/2 then only answer is 9/2.
How is it possible the answer is 9/2. If 4+1/2 then only answer is 9/2.
Muthu said:
9 years ago
@Ajax.
You answer is very simple. But I don't understand it please explain Clearly.
You answer is very simple. But I don't understand it please explain Clearly.
Folake said:
1 decade ago
I don't really understand this question. Some one should please help me out.
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