A boat covers 36 km downstream in 3 hours and maps the identical stretch upstream in 6 hours. Find the speed of the river stream current. MCQ with Answer and Explanation
Two outposts M and N are 320 km apart. Train A leaves M for N at 40 km/h at 6:00 AM. Train B leaves N for M at 60 km/h at 8:00 AM. At what time will they cross?
Explanation:
Let speed of current be c. 24 / (9 + c) + 24 / (9 - c) = 6. Dividing by 6: 4 / (9 + c) + 4 / (9 - c) = 1 => 4(9 - c + 9 + c) = 81 - c^2 => 72 = 81 - c^2 => c^2 = 9 => c = 3 km/h.
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