# The boat sailed from one pier to another against the river flow in 4 hours. The return trip took her 3 hours.

The boat sailed from one pier to another against the river flow in 4 hours. The return trip took her 3 hours. The speed of the river is 1 km / h. Find the boat’s own speed and the distance between the marinas.

Let us denote the distance between the piers through S, the boat’s own speed through V, and the speed of the river through W.
By the condition of the problem, it is known that W = 1 km / h.
The boat speed along the river V1 is equal to the sum of the boat’s own speed and the speed of the river flow:
V1 = V + W = V + 1.
Then we can write the equation:
S = V1 * 3 = 3 * (V + 1).
The speed of the boat against the river flow V2 is equal to the difference between its own speed and the speed of the river flow:
V2 = V – W = V – 1.
From here we get the second equation:
S = V2 * 4 = 4 * (V – 1).
Therefore, we have:
S = 3 * (V + 1) = 4 * (V – 1),
3 * V + 3 = 4 * V – 4,
V = 7.
S = 3 * (V + 1) = 3 * (7 + 1) = 24.
Answer: V = 7 km / h, S = 24 km.

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