Aptitude - Boats and Streams - Discussion
Discussion Forum : Boats and Streams - General Questions (Q.No. 15)
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 |
Discussion:
48 comments Page 1 of 5.
Supriyo Mondal said:
3 years ago
Dw : Up.
Ratio of speed = 4 : 3,
Ratio of time = 3: 4,
= 6h : 8h ( Total time 14 hrs).
Then speed = 8kmph : 6 kmph,
Now speed of stream = 1/2 ( 8-6) = 1 kmph.
Ratio of speed = 4 : 3,
Ratio of time = 3: 4,
= 6h : 8h ( Total time 14 hrs).
Then speed = 8kmph : 6 kmph,
Now speed of stream = 1/2 ( 8-6) = 1 kmph.
(29)
Vicky said:
4 years ago
He finds that he can row 4 km with the stream in the same time as 3 km against the stream.
So,4 -3 = 1.
So,4 -3 = 1.
(8)
Raihan said:
4 years ago
Let speed in still water be x.
Let the speed of the stream be y.
So, 48/ (x+y) +48/ (x-y) =14 ---> equation(1)
And;
4/(x+y) =3/ (x-y)--> equation(2).
Solving the above two equations,
We get,
y = 1, Which is the answer.
Let the speed of the stream be y.
So, 48/ (x+y) +48/ (x-y) =14 ---> equation(1)
And;
4/(x+y) =3/ (x-y)--> equation(2).
Solving the above two equations,
We get,
y = 1, Which is the answer.
(5)
Jamshaid said:
3 years ago
The solution has been imposed by supposing values.
[(48/(X+Y) + 48/(X-Y)] = 14 hrs,
Total time down- & up-, stream
X/Y = 7, Ratio of Speed.
Hence Y = X/7.
Putting Y = X/7 in Eq I.
[(48/(X+X/7) + 48/(X-X/7)] = 14, on simplifying the following quadratic form is obtained.
6.85X^2 - 48X - 0.
Using coefficients in quadratic equation; X = [-b +-(b^2 - 4ac)]/2a.
X = 7 hence Y = 1, as X/Y = 7.
[(48/(X+Y) + 48/(X-Y)] = 14 hrs,
Total time down- & up-, stream
X/Y = 7, Ratio of Speed.
Hence Y = X/7.
Putting Y = X/7 in Eq I.
[(48/(X+X/7) + 48/(X-X/7)] = 14, on simplifying the following quadratic form is obtained.
6.85X^2 - 48X - 0.
Using coefficients in quadratic equation; X = [-b +-(b^2 - 4ac)]/2a.
X = 7 hence Y = 1, as X/Y = 7.
(3)
Jamshaid said:
3 years ago
How X/Y = 7?
By simplifying (X+Y) / (X-Y) = 4/3.
Please explain.
By simplifying (X+Y) / (X-Y) = 4/3.
Please explain.
(3)
Rrr said:
4 years ago
Why 8-6 and why not 8+6 is taken? Explain please.
(3)
Rrr said:
4 years ago
@Raihan.
How do we solve those two equations? Please explain that too.
How do we solve those two equations? Please explain that too.
(3)
Loveleen Punni said:
5 years ago
@Rohit
So as given in the question, " he can row 4 km with the stream in the same time as 3 km against the stream" means that downward stream time is equal to upward stream time.
Therefore, 4/u+v = 3/u-v (distance/speed=time)
4u-4v = 3u+3v,
4u-3u = 3v+4v,
u = 7v,
u/v = 7/1.
Hence, v = 1km/hr.
So as given in the question, " he can row 4 km with the stream in the same time as 3 km against the stream" means that downward stream time is equal to upward stream time.
Therefore, 4/u+v = 3/u-v (distance/speed=time)
4u-4v = 3u+3v,
4u-3u = 3v+4v,
u = 7v,
u/v = 7/1.
Hence, v = 1km/hr.
(3)
Souvik masanta said:
5 years ago
He takes the same time for the 4 km with stream and 3 km against the stream
so,
Distance/speed = time.
4 /(x+y) = t ---> (1)
3/(x-y)= t ---> (2).
So, 4/(x+y)=3/(x-y).
x/y=7/1.
So, the rate of the stream =1km/h.
so,
Distance/speed = time.
4 /(x+y) = t ---> (1)
3/(x-y)= t ---> (2).
So, 4/(x+y)=3/(x-y).
x/y=7/1.
So, the rate of the stream =1km/h.
(3)
Nikalus said:
1 year ago
Thank you all for explanation
(1)
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