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:
65 comments Page 2 of 7.
Sai said:
8 years ago
We know that.
Still in water + stream = downstream.
In question downstream distance and time is given, we get the downstream speed and still in water speed also given.
Then we can find the stream speed easily.
Still in water + stream = downstream.
In question downstream distance and time is given, we get the downstream speed and still in water speed also given.
Then we can find the stream speed easily.
(2)
Sivaraj Pandian said:
10 months ago
Thank You @Padmagadi.
(1)
Sowmya.G said:
9 years ago
Speed= 15km/hr
Distance= 30 km/hr
Time= distance/speed
Speed of stream (v) is taken as x
Speed of boat in still water(u)=15km/hr
So,
Speed upstream=(15-x) km/hr.
Speed downstream=(15+x)km/hr.
30/15+x + 30/15-x=4 1/2(this is equation is written with the help of, time= distance/speed)
Further calculations are made. So we get x=5 km/hr.
Distance= 30 km/hr
Time= distance/speed
Speed of stream (v) is taken as x
Speed of boat in still water(u)=15km/hr
So,
Speed upstream=(15-x) km/hr.
Speed downstream=(15+x)km/hr.
30/15+x + 30/15-x=4 1/2(this is equation is written with the help of, time= distance/speed)
Further calculations are made. So we get x=5 km/hr.
(1)
Geetha said:
8 years ago
How 900 came? Explain.
(1)
Darshana Jain said:
10 years ago
Thank you very much for the given explanation.
AdityaLath said:
1 decade ago
Short trick:
D = z(x^2-y^2)/2x.
Where.
D = Distance.
Z = Time taken.
x = Speed of boat in still water.
y = Speed of stream.
30 = 9*(15^2-y^2)/2*2*15.
200 = 225-y^2.
y^2 = 25.
y = 5 answer.
D = z(x^2-y^2)/2x.
Where.
D = Distance.
Z = Time taken.
x = Speed of boat in still water.
y = Speed of stream.
30 = 9*(15^2-y^2)/2*2*15.
200 = 225-y^2.
y^2 = 25.
y = 5 answer.
Sneha said:
1 decade ago
How you people got 9/2? Please explain that.
Anjali said:
1 decade ago
Please explain it in an easy way, which will be helpful for me.
Ranjith said:
1 decade ago
4 hours and 30 minutes as 9/2. Total in terms of km/ hr.
Muthu said:
1 decade 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.
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