Question
The ratio of the speed of boats βAβ and βBβ in
still water is 8:9, respectively. The speed of the current is 25% of the speed of boat βAβ in still water. If boat βAβ takes 8 hours to travel 640 km downstream, then find the time taken by boat βBβ to travel 168 km upstream and 880 km downstream. (Note: Both the boats are rowing in the same stream.)Solution
Let the speeds of boats βAβ and βBβ in still water be 8x km/hr and 9x km/hr Therefore, speed of the current = 0.25 Γ 8x = 2x km/hr According to the question, 8x + 2x = 640/8 Or, 10x = 80 Or, x = 8 Therefore, upstream speed of boat βBβ = 9x β 2x = 7x = 56 km/hr Downstream speed of boat βBβ = 9x + 2x = 11x = 88 km/hr Required time taken = (168/56) + (880/88) = 3 + 10 = 13 hours
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