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:
64 comments Page 3 of 7.
Sneha said:
10 years ago
How you people got 9/2? Please explain that.
AdityaLath said:
10 years 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.
Darshana Jain said:
9 years ago
Thank you very much for the given explanation.
Srinivas said:
9 years ago
Nice explanation @Seetha.
Krishna said:
9 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.
Rohit said:
9 years ago
How came 4(1/2)?
Praveenbehera said:
9 years ago
Good explanation @Seetha. Thanks.
Priya said:
8 years ago
The speed of the current is 5 then the speed of the boat in downstream =u+v =15+5 =20;.
The speed of the boat in upstream = u-v = 15-5 =10;.
Time =distance/speed.
4 1/2 = 30/20+30/10.
9/2=9/2.
The speed of the boat in upstream = u-v = 15-5 =10;.
Time =distance/speed.
4 1/2 = 30/20+30/10.
9/2=9/2.
Roneet Jena said:
10 years ago
[(450-30x)+(450+30x)]/(225-x^2) = [900/(225-x^2)].
Gourav Shervegar said:
8 years ago
Why the speed of upstream is 15-x and speed of downstream is 15+x?
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