Aptitude - Boats and Streams - Discussion

Discussion Forum : 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:
3 km/hr
5 km/hr
8 km/hr
9 km/hr
Answer: Option

Speed in still water = 1 (11 + 5) kmph = 8 kmph.

Video Explanation: https://youtu.be/KQX_mA3tcVA

38 comments Page 1 of 4.

Dhanmoni said:   1 year ago
In one hour, the boat goes the downstream = 11 km/h
On the other hand, the boat goes the upstream = 5 km/h,
So, the speed of the b.in still water is = d+u÷ 2.
= 11+5÷2
= 8 km/ h => answer.

Musoyiti said:   4 years ago
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.

A.K.BALAKRISHNAN said:   4 years ago

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.

Thank you.

Vinau said:   5 years ago
X+Y+X-Y=11 + 5,

Then, X=8.

Darkele said:   5 years ago
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.

Shandeepsamy said:   5 years ago
Where this 1/2 came from? Please explain.

HARI said:   5 years ago
For finding the speed of the boat in still water = (upstream-downstream/2).
For finding water speed = (upstream+downstream/2).

Nurun Nobi Khokon said:   6 years ago
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].

Rz reddy said:   6 years ago
Upstream so(U).
D+U = 11.
D-U = 5.
2D = 16.
D = 16/2.
D = 8km/hr.

Yamini said:   6 years ago
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.

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