Aptitude - Boats and Streams - Discussion

hi ! @Vijaya.

In question, it will be already provided the keyword like upstream or downstream and With stream or Against Stream.

With stream = a+b(speed of d object in still water +speed of d stream) => Down stream.

Against stream = a-b(speed of d object in d still water - speed of d stream) => up stream.

Given:

Speed downstream, a = 15 km/h.
Rate of current, v = 2.5 km/h.

We need to find the value of b, i.e. speed upstream (Speed against the current).

As we know that, speed downstream, a = u+v.
Substituting the value of a and v;

15 = u+2.5.
u = 12.5 km/h.

Now as u = 12.5 km/h and v = 2.5 km/h.
So, speed upstream, b = u-v.

b = 12.5-2.5.
b = 10 km/h answer.

So the right answer is 10 km/h.

A man speed with the current means A man moving along with water, means it is downstream(d) speed = 15 km/hrs.

Rate of current or stream (s) = 2.5 km/hrs.

So,

From the downstream formula (d) = b + s.

We know the d and s values, so substitute those values in the above formula and obtain the b value i.e.

b = 15-2.5 ==> 12.5 kh/hrs.

So we need to calculate the man's speed against the water it will happen in upper stream (u) = b - s.

=> 12.5-2.5 ==> 10 km/hrs.

Let me clear first. What is meant by "Current"? Please any 1 explain it?

This is for @Vijaya.

Suppose there is a river which is flowing from left to right. And if you are swimming left to right. Your speed + River's speed i.e. downstream (with stream).

And if you are swimming from right to left. Your speed - Speed of river upstream (against the river i.e since you are swimming against the upstream speed.

Hai I'm not understanding this type of boats and streams problems I don't know what is meant by current speed like that please any one can explain me?

Why was the speed subtracted. I think it should be added.

For downstream. If we consider velocity of man and velocity of water as vector quantities.

Then velocity of man we are at the stream i.e Stream = Velocity of man we are at ground - Velocity of stream we are at ground.

15 I = x - 2.5 I.

x = 17.5 I.

Can anyone explain my doubt?

Can anybody explain me the meaning of question clearly. It's to confusing for me.

Man's speed with the current means downstream speed i.e. 15 km/ph.

The speed of current means speed of stream i.e 2.5 km/ph.

Man's speed against the current means upstream.

Now we have to find upstream speed.

Speed in current = 1/2 (downstream speed - upstream speed).

2.5 = 1/2 (15 - x).

5 = 15 - x.

-10 = -x.

x = 10 km/ph.