A boat goes 27 km upstream and 33 km downstream in 6 hours. In the same time it can go 36 km upstream and 22 km downstream. How much time will it take to go 36 km upstream and 44 km downstream?
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8 h 10 m
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8 h 50 m
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7 h 50 m
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8 h
D
Correct answer
Explanation
Let upstream speed = b-s and downstream speed = b+s. From the given conditions, we can set up two equations: 27/(b-s) + 33/(b+s) = 6 and 36/(b-s) + 22/(b+s) = 6. Solving these gives upstream speed = 9 km/h and downstream speed = 11 km/h. The required time is 36/9 + 44/11 = 4 + 4 = 8 hours.