A swimmer swims from a point P against the current for 6 min and then swims back along the current for next 6 min and reaches at a point Q. If the distance between P and Q is 120 m then the speed of the current (in km/h) is:

0.6

We know that,

A) While rowing upstream, the upstream speed is the difference between the speed of the boat in still water and the speed of the flow.

B) While rowing downstream, the downstream speed is the addition of the speed of the boat in still water and the speed of the flow.

C) Distance = Time × Speed

We have,

A swimmer swims from point P against the current for 6 min and then swims back along the current for next 6 min and reaches at a point Q.

The distance between P and Q = 120 m.

Let's suppose the swimmer started from P and swam 360 seconds to R against the current, then return to Q swimming for 360 seconds.

Let the speed of the swimmer in still water and the current be U and V m/s respectively.

​According to the question,

PR = 360(U - V)      ....(x)

QR = 360(U + V)      ....(y)

So, PQ = QR - PR

= 120 = 360(U + V - U + V) (From x and y)

So, the speed of the current = V = \(\frac{1}{6}\) m/s

Now, the speed of the current = \(\frac{1}{6}\) × \(\frac{18}{5}\) = 0.6 km/h