A boat goes 24 km downstream and returns upstream. Its speed in still water is 9 km/h and the stream flows at 3 km/h. How long does the whole trip take (in hours)?
Answer and explanation
Correct answer: A. 6
- Step 1: Downstream speed = 12 km/h, upstream speed = 6 km/h. Step 2. Time = 24/12 + 24/6 = 6 hours. Answer: 6. Why not the others: 5.3 is what you get if you ignore the stream. 2 is what you get if you count only the downstream leg. 8 is what you get if you use the upstream speed for both legs.
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