A boat running upstream covers 10 km in 30 minutes, and running downstream covers the same 10 km in 25 minutes. Find the speed of the water current (in km/h).

Introduction / Context:
Equal distances allow conversion of times to effective speeds; the current is half the difference of downstream and upstream speeds.

Given Data / Assumptions:

• Upstream: 10 km in 30 min = 0.5 h ⇒ vu = 20 km/h
• Downstream: 10 km in 25 min = 25/60 h ⇒ vd = 10 / (25/60) = 24 km/h

Concept / Approach:
Current c = (vd − vu)/2 and still-water speed b = (vd + vu)/2.

Step-by-Step Solution:

Verification / Alternative check:
Check times: 10/24 ≈ 0.4167 h (25 min) and 10/20 = 0.5 h (30 min).

Why Other Options Are Wrong:
3, 1, 0.5 do not reflect the half-difference of 24 and 20 which is exactly 2.

Common Pitfalls:
Using average time instead of converting each leg to a speed first, which is cleaner here.

Final Answer:
2 km/h.