Downstream distance in a fixed time: A boat's still-water speed is 15 km/h and the current is 3 km/h. How far does it travel downstream in 12 minutes?

Introduction / Context:
Distance at a constant speed is speed * time. For downstream travel, add the current to the still-water speed. Convert minutes to hours for consistent units before multiplying.

Given Data / Assumptions:

• u = 15 km/h; v = 3 km/h ⇒ downstream = 18 km/h.
• Time = 12 minutes = 12/60 h = 0.2 h.

Concept / Approach:
Use D = (u + v) * t with t in hours to get distance in kilometers.

Step-by-Step Solution:
Downstream speed = 15 + 3 = 18 km/h.Distance = 18 * 0.2 = 3.6 km.

Verification / Alternative check:
18 km/h is 0.3 km per minute; for 12 minutes: 0.3 * 12 = 3.6 km.

Why Other Options Are Wrong:
2.4, 1.8, 1.2, 3.0 correspond to incorrect speed or time conversions.

Common Pitfalls:
Using still-water speed instead of downstream; forgetting to convert 12 minutes to 0.2 hours.

Final Answer:
3.6 km