Question

Теплоход по течению реки за 4часа проплыл 124 км пути . Сколько км пути за 7 часов против течения реки проплывет теплоход если скорость течения реки 3 км/час?

Answer 1

Скорость по течению
Vпо = Vс + Vт = 124 : 4 = 31 км/час.
Vпр = Vпо - 2*Vт = 31 - 2*3 = 25 км/час
Путь за 7 часов
S = 25 * 7 = 175 км - ОТВЕТ

Answer 2

Problem Analysis

We are given that a boat traveled 124 km downstream in 4 hours. We need to find out how far the boat will travel upstream in 7 hours against a river current of 3 km/h.

Downstream Speed Calculation

To find the speed of the boat downstream, we can divide the distance traveled by the time taken. In this case, the boat traveled 124 km in 4 hours, so the downstream speed is 124 km / 4 hours = 31 km/h.

Upstream Speed Calculation

To find the speed of the boat upstream, we need to subtract the speed of the river current from the speed of the boat in still water. Let's denote the speed of the boat in still water as x km/h. The speed of the river current is given as 3 km/h.

When the boat is traveling upstream, its effective speed is reduced by the speed of the river current. Therefore, the boat's speed upstream is (x - 3) km/h.

Relationship between Speed, Time, and Distance

The relationship between speed, time, and distance is given by the formula: distance = speed * time.

Upstream Distance Calculation

We are given that the boat will travel upstream for 7 hours. Using the relationship between speed, time, and distance, we can calculate the distance traveled upstream as follows:

distance upstream = (speed upstream) * (time upstream)

Substituting the values we have:

distance upstream = (x - 3) km/h * 7 hours

Solving for x

To find the value of x, we need to solve the equation for distance upstream. We know that the distance upstream is equal to 124 km. Therefore, we can set up the equation:

124 km = (x - 3) km/h * 7 hours

Simplifying the equation:

124 km = 7x - 21 km/h * hours

145 km = 7x

x = 20.71 km/h

Upstream Distance Calculation (continued)

Now that we have the value of x, we can calculate the distance traveled upstream:

distance upstream = (x - 3) km/h * 7 hours

distance upstream = (20.71 km/h - 3 km/h) * 7 hours

distance upstream = 17.71 km/h * 7 hours

distance upstream = 123.97 km

Answer

The boat will travel approximately 123.97 km upstream in 7 hours against a river current of 3 km/h.