Correcting a unit slip and finding downstream distance: A man can row upstream 36 km in 6 h. If his still-water speed is 8 km/h, how far can he go downstream in 10 h?

Introduction / Context:The original stem showed “36 m” in 6 h, which is inconsistent with km/h speeds. By the Recovery-First Policy, we minimally repair it to 36 km so the problem is solvable without changing its intent. With upstream speed known, we determine the current and then the downstream distance for the requested time.

Given Data / Assumptions:

• Upstream: 36 km in 6 h ⇒ 6 km/h.
• Still-water speed u = 8 km/h.
• Let current speed be v; downstream time required is 10 h.

Concept / Approach:Upstream speed u − v = 6 ⇒ v = u − 6. Then downstream speed u + v gives distance over 10 h.

Step-by-Step Solution:u − v = 6 ⇒ v = 8 − 6 = 2 km/h.Downstream speed = u + v = 8 + 2 = 10 km/h.Distance in 10 h = 10 * 10 = 100 km.

Verification / Alternative check:Check symmetry: up 6, down 10 ⇒ u = (6 + 10)/2 = 8, consistent; v = (10 − 6)/2 = 2.

Why Other Options Are Wrong:80, 90, 120, 150 assume different speeds or times that do not match u = 8, v = 2.

Common Pitfalls:Not repairing the unit typo; computing distance with still-water speed instead of downstream speed.

Final Answer:100 km