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.
A person can row 10 km/h in still water. If it takes him exactly twice as long to row upstream as to row downstream over the same stretch, find the speed of the current.
Explanation:
Let speed of current be c km/h. Downstream speed = 10 + c, Upstream speed = 10 - c. Given: 2 * (10 - c) = 10 + c => 20 - 2c = 10 + c => 3c = 10 => c = 10/3 = 3.33 km/h.
A regular passenger bus tracks a route divided into three equal segments. It runs the segments at 20 km/h, 30 km/h, and 60 km/h respectively. Find the average speed across the whole route.
Explanation:
Let each segment distance be 60 km. Total distance = 3 * 60 = 180 km. Total time = 60/20 + 60/30 + 60/60 = 3 + 2 + 1 = 6 hours. Average speed = 180 / 6 = 30 km/h.
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