A man can row 4.5 km/h in still water and he finds that it takes him twice as…
2024
A man can row 4.5 km/h in still water and he finds that it takes him twice as long to row up as to row down the river. The speed of the stream is
Answer: B. 1.5 km/h — Answer: 1.5 km/h Let the speed of the stream be s km/h. The man's speed in still water is 4.5 km/h. Downstream speed = 4.5 + s; upstream speed = 4.5 − s. For…
- A.
2.5 km/h
- B.
1.5 km/h
- C.
2 km/h
- D.
1.75 km/h
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Correct answer: B
Answer: 1.5 km/h
Let the speed of the stream be s km/h. The man's speed in still water is 4.5 km/h.
Downstream speed = 4.5 + s; upstream speed = 4.5 − s.
For the same distance d, time upstream = d/(4.5 − s) and time downstream = d/(4.5 + s). Given time upstream = 2 × time downstream, so 1/(4.5 − s) = 2/(4.5 + s).
Solve the equation: 4.5 + s = 2(4.5 − s) ⇒ 4.5 + s = 9 − 2s ⇒ 3s = 4.5 ⇒ s = 1.5 km/h.
Therefore, the speed of the stream is 1.5 km/h.