A man can swim at 3 km/h in still water. The stream’s speed is 2 km/h. How long will he take to swim to a point 10 km upstream and then return to the start (total time in hours)?

Introduction / Context:
Swimming problems mirror boat-and-stream logic. The effective speed differs upstream and downstream due to the current.

Given Data / Assumptions:

• Still-water speed b = 3 km/h
• Current c = 2 km/h
• Upstream speed vu = b − c = 1 km/h
• Downstream speed vd = b + c = 5 km/h
• Upstream distance = 10 km; downstream distance = 10 km

Concept / Approach:
Total time = time upstream + time downstream = distance/speed per leg.

Step-by-Step Solution:

Verification / Alternative check:
Speeds and distances are straightforward; arithmetic is direct and consistent.

Why Other Options Are Wrong:
Any alternative value fails to match both leg times computed from the known effective speeds of 1 km/h and 5 km/h.

Common Pitfalls:
Using average speed across unequal leg speeds; the correct method adds individual times, not averages the speeds.

Final Answer:
12 hrs.