Question

Расстояние между двумя городами 168 км. Из этих городов на встречу друг другу выехали товарный и скорый поезда. Через сколько часов эти поезда встретятся, если товарный поезд проходит это расстояние за 2,8 ч, а скорый поезд- за 2,1 ч?

Answer 1

1)168:2,8=60 км/ч скорость товарного поезда
2)168:2,1=80 км/ч скорость товарного поезда
3)60+80=140 км/ч скорость сближения поездов
4)168:140=через 1,2 часа встретятся
Ответ:  через 1,2 часа

Answer 2

Problem Analysis

We are given that the distance between two cities is 168 km. A freight train covers this distance in 2.8 hours, while a high-speed train covers it in 2.1 hours. We need to determine how many hours it will take for these trains to meet.

Solution

To find the time it takes for the trains to meet, we can use the concept of relative speed. The relative speed is the sum of the speeds of the two trains. We can then divide the distance between the cities by the relative speed to find the time it takes for the trains to meet.

Let's calculate the relative speed and the time it takes for the trains to meet.

Calculation

The freight train covers the distance of 168 km in 2.8 hours, so its speed is:

Freight train speed = Distance / Time = 168 km / 2.8 hours = 60 km/h

Similarly, the high-speed train covers the same distance in 2.1 hours, so its speed is:

High-speed train speed = Distance / Time = 168 km / 2.1 hours = 80 km/h

The relative speed of the two trains is the sum of their speeds:

Relative speed = Freight train speed + High-speed train speed = 60 km/h + 80 km/h = 140 km/h

Now, we can calculate the time it takes for the trains to meet by dividing the distance between the cities by the relative speed:

Time to meet = Distance / Relative speed = 168 km / 140 km/h = 1.2 hours

Therefore, the freight train and the high-speed train will meet after 1.2 hours.

Answer

The freight train and the high-speed train will meet after 1.2 hours.