The boat swam downstream in 3 hours the same distance that it swims in 9 hours upstream.

| June 17, 2021 | education

The boat swam downstream in 3 hours the same distance that it swims in 9 hours upstream. The speed of the river is 2 km / h. Calculate the speed of the boat in still water.

Let’s denote the boat’s own speed by the letter a. Then the boat will go downstream with a speed of (a + 2) km / h, and against the current – with a speed of (a – 2) km / h.

Let us express the path of the boat downstream: S = v * t; S = 3 (a + 2).

Let us express the path of the boat against the current: S = 9 (a – 2).

Since the path downstream and the path upstream are equal, we get the equation:

3 (a + 2) = 9 (a – 2).

3a + 6 = 9a – 18.

3a – 9a = -18 – 6.

-6a = -24.

6a = 24.

a = 24: 6 = 4 (km / h) – own speed of the boat.

The path of the boat upstream is 9 (a – 2) = 9 * (4 – 2) = 9 * 2 = 18 (km).

Answer: the speed of the boat in still water is 4 km / h, the boat covered 18 km against the current.



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