Question

Решить задачу по действиям:двигаясь по течению реки,расстояние в 72 км теплоход проходит за 3 часа,а плот-за 18 часов.Какова скорость теплохода при движении против течения?

Answer 1

72:18=4(км/ч) - скорость плота и скорость течения (плот плывет только по течению)
72:3=24(км/ч) - скорость теплохода по течению
24-4=20(км/ч) - скорость теплохода против течения.

Answer 2

Problem Analysis

We are given that a boat travels a distance of 72 km downstream in 3 hours and a raft covers the same distance in 18 hours. We need to find the speed of the boat when it is moving upstream.

Solution

Let's assume the speed of the boat in still water is x km/h and the speed of the current is y km/h.

When the boat is moving downstream, its effective speed is the sum of its speed in still water and the speed of the current. So, the boat's effective speed downstream is (x + y) km/h.

Similarly, when the boat is moving upstream, its effective speed is the difference between its speed in still water and the speed of the current. So, the boat's effective speed upstream is (x - y) km/h.

We can set up the following equations based on the given information:

1. Downstream speed: (x + y) = 72/3 = 24 km/h. 2. Upstream speed: (x - y) = 72/18 = 4 km/h.

To find the speed of the boat in still water (x), we can solve these equations simultaneously.

Solving the Equations

Adding the two equations, we get: (x + y) + (x - y) = 24 + 4 Simplifying, we have: 2x = 28 Dividing both sides by 2, we find: x = 14 km/h

Therefore, the speed of the boat in still water is 14 km/h.

Answer

The speed of the boat when moving upstream against the current is 14 km/h.

Please let me know if you need any further clarification.