The distance between the two points is 3.6 km, we swam downstream in 30 minutes

| January 24, 2021 | education

The distance between the two points is 3.6 km, we swam downstream in 30 minutes, and upstream in 40 minutes. Determine the speed of the river. How many hours will the rafts travel the same distance?

1) According to the condition of the problem, the time of movement of the raft along the river is 30 minutes, that is, 0.5 hour. And the distance between the two points is 3.6 km. Let’s calculate the speed along the river. We get: 3.6 / 0.5 = 7.2 km / h.

2) From the condition of the problem it is known that the time of movement of the raft against the stream of the river is 40 minutes, that is, 2/3 hours. And the distance between the two points is still 3.6 km. Let’s calculate the speed upstream of the river. We get: 3.6 / 2/3 = 36/10 * 3/2 = (18 * 3) / (10 * 1) = 54/10 = 5.4 km / h.

3) Find the speed of the raft: (7.2 – 5.4) / 2 = 1.8 / 2 = 0.9 km / h.

4) 3.6 / 0.9 = 4 hours.

Answer: 0.9 km / h. – the speed of the river; in 4 hours – the rafts will cover a distance of 3.6.



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