- A13.33 km/h
- B15 km/h
- C12.5 km/h
- D10 km/h
Step-by-Step Solution
Up: 20 ÷ 10 = 2 h. Down: 20 ÷ 20 = 1 h. Average = 40 ÷ 3 = 13.33 km/h — less than the still-water speed, never equal to it.
Answer: A) 13.33 km/h
A patrol boat that does 15 km/h in still water goes 20 km up a river flowing at 5 km/h and then 20 km back. What is its average speed over the whole 40 km?
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