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:

Answer: Option D

Understanding the Problem:
Imagine a swimmer swimming in a river. The river's current pushes the swimmer, affecting their speed.
The swimmer swims against the current (meaning the current slows them down) for 6 minutes, then turns around and swims with the current (the current speeds them up) for another 6 minutes.
The total distance covered during this time is 120 meters.
We need to find the speed of the river's current.

Breaking it Down:
Let's say the swimmer's speed in still water is 'x' m/min and the speed of the current is 'y' m/min.
When swimming against the current, the effective speed is (x - y) m/min (because the current slows them down).
When swimming with the current, the effective speed is (x + y) m/min (because the current helps them).

Calculations:
Distance covered against the current = (x - y) * 6 minutes
Distance covered with the current = (x + y) * 6 minutes
The difference between these two distances is 120 meters (the distance between points P and Q):
[(x + y) * 6] - [(x - y) * 6] = 120
Simplifying this equation, we get:
6x + 6y - 6x + 6y = 120
12y = 120
y = 10 m/min

Converting to km/h:
We have the speed of the current as 10 m/min. To convert this to km/h, we need to multiply by 60 (minutes in an hour) and divide by 1000 (meters in a kilometer):
(10 m/min) * (60 min/hour) / (1000 m/km) = 0.6 km/h

Therefore, the speed of the current is 0.6 km/h.
The correct option is D.