Question

Решите задачу пж из двух городов, удаленных друг от друга на 1680 км, вышли одновременно навстречу друг другу 2 поезда. Первый поезд проходит это расстояние за 21 ч, а второй за 28 ч. через сколько часов поезда встретятся

Answer 1

1680:21=80км/ч скорость 1 поезда
1680:28=60км/ч скорость 2 поезда
80+60=140км/ч их общая скорость
1680:140=12ч они встретятся
ответ через 12ч

Answer 2

Скорость первого поезда 1680/21=80 км/ч
Скорость второго поезда 1680/28=60 км/ч
Так как они движутся навстречу друг другу их скорости складываются. Сумма будет равна 80+60=140 км/ч
Поезда встретятся через 1680/140=12 часов
Ответ: 12

Answer 3

Problem Analysis

We have two trains traveling towards each other from two cities that are 1680 km apart. The first train takes 21 hours to cover the distance, while the second train takes 28 hours. We need to determine how many hours it will take for the trains to meet.

Solution

To find the time it takes for the trains to meet, we can use the formula:

Time = Distance / Speed

Let's calculate the speeds of the trains first. The speed of the first train can be calculated by dividing the distance by the time it takes to cover that distance:

Speed of first train = Distance / Time = 1680 km / 21 hours

Similarly, the speed of the second train can be calculated as:

Speed of second train = Distance / Time = 1680 km / 28 hours

Now that we have the speeds of both trains, we can calculate the time it takes for them to meet. Since they are traveling towards each other, their speeds will add up:

Total speed = Speed of first train + Speed of second train

Let's substitute the values and calculate the total speed:

Total speed = (1680 km / 21 hours) + (1680 km / 28 hours)

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

Time = Distance / Total speed = 1680 km / ( (1680 km / 21 hours) + (1680 km / 28 hours) )

Let's calculate the value:

Time = 1680 km / ( (1680 km / 21 hours) + (1680 km / 28 hours) )

Using a calculator, we can find the value of the expression:

Time ≈ 10.5 hours

Therefore, the trains will meet approximately 10.5 hours after they start their journey.

Answer

The trains will meet approximately 10.5 hours after they start their journey.