Discussion :: Boats and Streams - General Questions (Q.No.5)
In one hour, a boat goes 11 km/hr along the stream and 5 km/hr against the stream. The speed of the boat in still water (in km/hr) is:
Answer: Option C
Video Explanation: https://youtu.be/KQX_mA3tcVA
|Ashok said: (Jul 19, 2011)|
|From where do this 1/2 came from?|
|Vivek Patidar said: (Sep 5, 2011)|
|Because in the condition of still position of water the speed one side and opposite side of water will be equal thats why we will take average of both speed.|
|Manjit Singh said: (Sep 15, 2011)|
|Here speed along the stream and against the stream is given. Then how can we assume water to be steady (both the ways). Then why this 1/2 has come?|
|Debapriya Dandapat said: (Sep 17, 2011)|
|Upstream relative speed is u + v=11km/hr
Downstream speed is u-v=5
Where u= speed of boat in still water and v is speed of stream
So adding two equations u+v + u-v =11+5
|Ajit Jha(Iit Kharagpur) said: (Dec 30, 2011)|
|This Q is wrong buddy...
Here in stream dir. it takes 1 hour and again in downstream it takes 1 hour.
fm eq. 1 & 2.. we get..
|Saloni Nautiyal said: (Feb 25, 2012)|
|Formula for speed of boat in still water=[(X+Y)+(X-Y)]/2
where X=SPEED OF BOAT IN STILL WATER
Y=SPEED OF STREAM/CURRENT
ANSWER IS NOT IN THE OPTIONS
|Kottitheking said: (Sep 9, 2012)|
|Upstream relative speed is u + v=11km/hr
Downstream speed is u-v = 5
Where u = speed of boat in still water and v is speed of stream
Then adding two equations u+v + u-v =11+5
|Brinda Iyer said: (Mar 10, 2013)|
|But if in the same question distance traveled is asked, then what is the formula?|
|Ritha Epsiba said: (Mar 13, 2013)|
|If the speed of a boat in still water is u km/hr and the speed of the stream is v km/hr, then:
Speed downstream = (u + v) km/hr.
Speed upstream = (u - v) km/hr.
|Arun.D said: (Jun 3, 2013)|
Speed in still water = 1/2(a + b) km/hr.
a = upstream.
b = downstream.
Speed = 1/2(11+5)km/hr.
|Mina said: (Jan 7, 2015)|
|What is u and v?|
|Subaram said: (Jan 8, 2015)|
|Here direction along the stream called downstream and against the stream called upstream. In this question they gave along the stream 11 kmhr against the stream 5 kmhr. So speed still in water = 1/2 (a+b) , here a downstream be up stream as for formula.|
|Naresh said: (Apr 28, 2015)|
Speed in the downstream (d) = 11 km/hr.
Speed in the upstream (u) = 5 km/hr.
Speed of the Boat in still water = d + u/2.
=> 11 + 5/2 = 16/2.
=> 8 km/hr.
|Ramachandran said: (May 28, 2015)|
|Hello guys how would you find:
11 km/hr is Downstream.
5 km/hr is Upstream.
|Suchita said: (Aug 9, 2015)|
|Because in question they have mentioned speed of boat along the stream (i.e downstream) is 11km/hr and against the stream (i.e upstream) is 5km/hr.|
|Nikul Rana said: (Nov 1, 2015)|
|Speed downstream = X+Y = 11 kmph;
Speed upstream = X-Y = 5 kmph;
Speed of the still water = (X+Y)+(X-Y)*1/2 = 8 kmph.
|Priya said: (Dec 10, 2015)|
|What is this? Am not clear, I am late pick up person, say clearly guys.|
|Nija said: (Jan 18, 2016)|
|In this question, it is not mentioned whether 1 hour each taken by downstream and upstream. So how can we solve this questions ? Please am confused.|
|Ayan said: (Apr 13, 2016)|
|The question is not clear. It says in one hour both travel upstream as well as downstream. How is it explain me?|
|Shruti said: (Jun 22, 2016)|
|How come the speed becomes 11 kmph and 5 kmph when only distance is given, and boat travels both the distances in total 1 hour?
I think either the question is wrong or 8 is not the answer.
|Shudhu said: (Jul 31, 2016)|
|Downstream so, x + y = 11.
Upstream so, x - y = 5.
Solve equation 1 and 2.
You get x =7.5.
So, nearest answer is 8.
|Sara said: (Jan 2, 2017)|
|x = speed of stream still in water.
y = speed of stream.
downstream = Distance/ X+Y = Time,
= 11/ X+Y = 1hour.
Upstream= Distance/ X-Y = Time.
= 5/X-Y = 1hour.
11 = X + Y -----(1)eq
5 = X - Y ------(2)eq
We need x, so cancel y.
2X = 16,
X = 8kmph.
|Aman Kumar said: (Jan 27, 2017)|
|B = Speed of boat.
w = Speed of water.
B + W=11 (with the stream)
B - W=5 (opp to stream)
= 8 KMPH.
|Suresh said: (Feb 26, 2017)|
|A boats cover 1 km in 10 minute with stream and 1 km in 20 minute against stream now speed of boat in still water will be?
Please solve it.
|Audry said: (Mar 15, 2017)|
|Let U= speed of boat in still water and v=speed of stream then;
Upstream speed, U - V = 5km/hr,
Downstream speed, U + V = 11km/hr,
U + V + U - V = 11 + 5
2U = 16
U = 16/2 = 8km/hr.
|Satish said: (Jun 17, 2017)|
8=X (stream speed).
|Bhavesh said: (Aug 12, 2017)|
|What is this same Q is like in 3 hours a boat goes 11 km along the stream and 5 km against the stream the speed of the boat in still water is?|
|Kamala Kant said: (Sep 11, 2017)|
|Do you have the concept of eqillibrium? then say
if , (11/x +y) + (5/x-y) =3,
|Yamini said: (Oct 26, 2017)|
|If the speed downstream is a km/hr and speed upstream is b km/hr then,
Speed in still water=1/2(a+b)km/hr.
|Rz Reddy said: (Nov 4, 2017)|
D+U = 11.
D-U = 5.
2D = 16.
D = 16/2.
D = 8km/hr.
|Nurun Nobi Khokon said: (May 23, 2018)|
|Let, downstream (with stream) speed= x.
upstream (against) speed is= y.
x = speed of the boat+speed of the water.
y = speed of the boat-speed of water.
x+y = 2*speed of the boat.
So, speed of the boat = (x+y)/2 [downstream speed+upstream speed].
|Hari said: (Jun 11, 2018)|
|For finding the speed of the boat in still water = (upstream-downstream/2).
For finding water speed = (upstream+downstream/2).
|Shandeepsamy said: (Jul 2, 2018)|
|Where this 1/2 came from? Please explain.|
|Darkele said: (Jul 4, 2018)|
|Note, there is no use of the 1 hour given because the upstream and downstream is sufficient to get the speed of the boat in still water.|
|Vinau said: (Sep 5, 2018)|
X+Y+X-Y=11 + 5,
|A.K.Balakrishnan said: (Sep 13, 2019)|
Follow this method for all boat question;
Downstream means boat towards the down in this situation we have to find the speed of boat and speed of stream.
Let x be boat speed.
Let y be stream speed.
1) Down stream speed = D/T(downstream time) = x+y
note: distance will be the same as both the streams.
2) Upper stream speed = D/T (upper stream time) = x-y.
|Musoyiti said: (Jun 6, 2020)|
|My way of solving is that;
Let the speed of the current be x.
So the speed in still water will be 11-x and 5 +x. Now as these both expressions are same so we use linear equation and find the value of x to be 3. So the speed of the current is 3 km/hr. So the speed of the boat in still water is 11-3=8.
Hence it is 8 km/hr.
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