Aptitude - Boats and Streams - Discussion

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.

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.

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.

hi ! @Vijaya.

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