The boat swam down the river for 30 km in the same time as 20 km upstream.

| September 5, 2021 | education

The boat swam down the river for 30 km in the same time as 20 km upstream. How far will the rafts travel in the same time?

1. Let the boat sailed 30 km and 20 km in time t. Let’s denote the speed of the boat v (cat), and the speed of the current v (flow). Then the speed of the boat downstream is equal to v (cat) + v (flow), and the speed of the boat upstream is equal to v (cat) – v (flow).
We have a system of equations:
{30 / t = v (cat) + v (flow) (1);
{20 / t = v (cat) – v (flow) (2);
2. Subtract from equation (1) equation (2);
30 / t – 20 / t = v (cat) + v (flow) – v (cat) – v (flow);
10 / t = 2 * v (flow);
v (flow) = 5 / t;
3. It turns out that the speed of the current is 5 / t km / h. The rafts will sail 5 km in time t.
4. Answer: the rafts will sail 5 km.



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