A man can row 4.5 km/hr in still water and he finds that it takes him twice as…
2024
A man can row 4.5 km/hr 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
- A.
2.5 km/hr
- B.
1.5 km/hr
- C.
2 km/hr
- D.
1.75 km/hr
Attempted by 19 students.
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Correct answer: B
Answer: 1.5 km/hr
Let x be the speed of the stream (km/hr). Then downstream speed = 4.5 + x and upstream speed = 4.5 - x.
Use the condition that rowing upstream takes twice as long as rowing downstream: d/(4.5 - x) = 2d/(4.5 + x).
Cancel d on both sides to get 1/(4.5 - x) = 2/(4.5 + x). Cross-multiply: 4.5 + x = 2(4.5 - x).
Solve the equation: 4.5 + x = 9 - 2x → 3x = 4.5 → x = 1.5 km/hr.
Thus the speed of the stream is 1.5 km/hr.