A man can swim downstream at 8 km/h and upstream at 2 km/h. Find the speed of…

Concept: For a swimmer/boat in a stream, the downstream speed equals the still-water speed plus the current's speed, and the upstream speed equals the still-water speed minus the current's speed. Subtracting the upstream speed from the downstream speed cancels the still-water speed and leaves exactly twice the current's speed: downstream − upstream = 2 × (current speed).

Application:

1. Given: downstream speed = 8 km/h and upstream speed = 2 km/h.

2. Difference = 8 − 2 = 6 km/h, which equals twice the current's speed.

3. Speed of current = 6 ÷ 2 = 3 km/h.

Cross-check: the still-water speed can be recovered as ½(8 + 2) = 5 km/h. Then 5 + 3 = 8 km/h matches the given downstream speed, and 5 − 3 = 2 km/h matches the given upstream speed — the figures are internally consistent.

So the speed of the current is 3 km/h, matching the option "3km/hr".