The raft sails from point A to point B in 30 hours, and the boat in 3 hours. How long will the boat

| March 19, 2021 | education

The raft sails from point A to point B in 30 hours, and the boat in 3 hours. How long will the boat take to cover the path from B to A.

The movement of the raft indicates the flow of the river in the direction from A to B. Let the distance between A and B = X km.

River flow speed = X / 30 km / h.

Boat speed downstream = X / 3 km / h.

The speed of the boat downstream is the combined speed of the river and the boat. This means that to get the speed of the boat against the current, the speed of the river flow must be subtracted twice:

(X / 3) – (2 * X / 30) = (5 * X – X) / 15 = 4 * X / 15 km / h.

The time it takes for the boat to pass from B to A:

X / (4 * X / 15) = 15 * X / (4 * X) = 15/4 = 3.75 hours = 3 hours 45 minutes.

Answer: a boat from point B to point A will take 3 hours and 45 minutes.



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