Question

Лодка по течению реки плывёт со скоростью 12 км/ч, а против 6 км/ч. Сколько времени должна плыть лодка по озеру, чтобы проплыть то же расстояние что и по течению реки за 3 ч?

Answer 1

12×3=36км расстояние которое проплыла лодка по течению 36:6=6ч она будет плыть против течения

Answer 2

Problem Analysis

We are given that a boat is traveling downstream in a river at a speed of 12 km/h and upstream at a speed of 6 km/h. We need to find the time it takes for the boat to travel the same distance on a lake as it does downstream in the river in 3 hours.

Solution

Let's assume the distance traveled by the boat downstream in the river is D km. Since the boat is traveling downstream, its effective speed is the sum of its own speed and the speed of the river current, which is 12 km/h. Therefore, the time taken to travel distance D downstream is given by:

Time taken downstream = D / (12 km/h) Similarly, when the boat is traveling upstream, its effective speed is the difference between its own speed and the speed of the river current, which is 6 km/h. Therefore, the time taken to travel distance D upstream is given by:

Time taken upstream = D / (6 km/h) We are given that the time taken to travel distance D downstream is 3 hours. Therefore, we can set up the following equation:

Time taken downstream = 3 hours

Substituting the values, we have:

D / (12 km/h) = 3 hours

Simplifying the equation, we can solve for D:

D = 3 hours * (12 km/h) = 36 km

Now, we need to find the time it takes for the boat to travel the same distance D on the lake. Since there is no current in the lake, the boat's speed is its own speed. Therefore, the time taken to travel distance D on the lake is given by:

Time taken on the lake = D / (12 km/h) = 36 km / (12 km/h) = 3 hours

So, the boat needs to travel for 3 hours on the lake to cover the same distance as it does downstream in the river in 3 hours.

Answer

The boat needs to travel for 3 hours on the lake to cover the same distance as it does downstream in the river in 3 hours.

Explanation

When the boat is traveling downstream in the river, its effective speed is the sum of its own speed and the speed of the river current, which is 12 km/h. When the boat is traveling upstream, its effective speed is the difference between its own speed and the speed of the river current, which is 6 km/h. By setting up the equation and solving for the distance traveled downstream, we find that the boat needs to travel for 3 hours on the lake to cover the same distance as it does downstream in the river in 3 hours.