Question

Два поезда едут навстречу друг другу.Скорость одного из них 80 км/ч ,а другого -в 1целая 1/7 раза меньше .Через сколько времени они встретятся, если сейчас между ними 70 км?

Answer 1

1) 80 ÷ 1 1/7=70 (км/ч) - скорость 2-го поезда
2) 80+70=150 (км/ч) - скорость сближения
3) 70÷150=7/15(ч)=28(мин).
Ответ: через 28 минут.

Answer 2

Problem Analysis

We have two trains traveling towards each other. The speed of one train is 80 km/h, while the speed of the other train is 1 and 1/7 times smaller. The distance between them is 70 km. We need to calculate the time it takes for them to meet.

Calculation

Let's denote the speed of the second train as x km/h. According to the problem, the speed of the second train is 1 and 1/7 times smaller than the speed of the first train. Therefore, we can write the equation:

x = (1 - 1/7) * 80

Simplifying the equation, we get:

x = (6/7) * 80

Now, we can calculate the time it takes for the trains to meet using the formula:

time = distance / relative speed

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

relative speed = 80 + x

Substituting the value of x into the equation, we get:

relative speed = 80 + (6/7) * 80

Now, we can calculate the time:

time = 70 / relative speed

Substituting the value of relative speed into the equation, we get:

time = 70 / (80 + (6/7) * 80)

Let's calculate the time using this equation.

Calculation Result

Using the given values, we can calculate the time it takes for the trains to meet:

time = 70 / (80 + (6/7) * 80)

Calculating this expression, we find that the time is approximately 0.625 hours.

Therefore, the two trains will meet in approximately 0.625 hours.

Please note that the above calculation assumes constant speeds for the trains and does not take into account any acceleration or deceleration.