Boats & Streams · Question 21 · Medium
Boats & Streams question 21
A boat covers 40 km downstream and 24 km upstream in 8 hours. It also covers 30 km downstream and 36 km upstream in 9 hours. What is the speed of the boat in still water?
- 8 km/h
- 2 km/h
- 6 km/h
- 10 km/h
Answer and explanation
Answer: A. 8 km/h
Explanation: Let 1/d = x and 1/u = y: 40x + 24y = 8 and 30x + 36y = 9. Solving gives x = 1/10, y = 1/6, so downstream 10 km/h and upstream 6 km/h. Still-water speed = (10 + 6)/2 = 8 km/h.
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