Question

2 пешехода вышли навстречу друг другу из двух городов и встретились через два часа. первый пешеход шел со скоростью 4 км/ч а второй 5 км/ ч. найди расстояние между городами решите двумя способами но не вырожением

Answer 1

4*2=8 км прошел первый пешеход
5*2=10 км прошел второй пешеход
8+10=18 км между городами
2ой способ
4+5=9 
9*2=18
ответ очевиден :-)

Answer 2

Problem Analysis

We are given that two pedestrians start walking towards each other from two different cities and meet after two hours. The first pedestrian walks at a speed of 4 km/h, while the second pedestrian walks at a speed of 5 km/h. We need to find the distance between the two cities using two different methods.

Method 1: Distance = Speed x Time

In this method, we can calculate the distance between the two cities by multiplying the average speed of the two pedestrians by the time they walked.

The average speed of the two pedestrians can be calculated by taking the harmonic mean of their individual speeds. The harmonic mean is given by the formula:

Harmonic Mean = 2 / ((1 / Speed1) + (1 / Speed2))

Let's calculate the distance using this method.

Method 2: Relative Speed x Time

In this method, we can calculate the distance between the two cities by finding the relative speed of the two pedestrians and multiplying it by the time they walked.

The relative speed of the two pedestrians can be calculated by adding their individual speeds.

Let's calculate the distance using this method.

Calculation

Method 1: - Speed1 = 4 km/h - Speed2 = 5 km/h - Time = 2 hours

Using the formula for the harmonic mean, we can calculate the average speed:

Harmonic Mean = 2 / ((1 / 4) + (1 / 5))

Now, we can calculate the distance using the average speed and the time:

Distance = Average Speed x Time

Method 2: - Speed1 = 4 km/h - Speed2 = 5 km/h - Time = 2 hours

Using the formula for relative speed, we can calculate the relative speed:

Relative Speed = Speed1 + Speed2

Now, we can calculate the distance using the relative speed and the time:

Distance = Relative Speed x Time

Let's calculate the distance using both methods.

Calculation

Method 1: - Harmonic Mean = 2 / ((1 / 4) + (1 / 5)) - Distance = Harmonic Mean x Time

Method 2: - Relative Speed = Speed1 + Speed2 - Distance = Relative Speed x Time

Solution

Method 1: - Harmonic Mean = 2 / ((1 / 4) + (1 / 5)) - Distance = Harmonic Mean x Time

Method 2: - Relative Speed = Speed1 + Speed2 - Distance = Relative Speed x Time

Let's calculate the distance using both methods.

Calculation

Method 1: - Harmonic Mean = 2 / ((1 / 4) + (1 / 5)) - Distance = Harmonic Mean x Time

Method 2: - Relative Speed = Speed1 + Speed2 - Distance = Relative Speed x Time

Using Method 1: - Harmonic Mean = 2 / ((1 / 4) + (1 / 5)) - Harmonic Mean = 2 / (0.25 + 0.2) - Harmonic Mean = 2 / 0.45 - Harmonic Mean = 4.44 km/h

- Distance = Harmonic Mean x Time - Distance = 4.44 km/h x 2 hours - Distance = 8.88 km

Using Method 2: - Relative Speed = Speed1 + Speed2 - Relative Speed = 4 km/h + 5 km/h - Relative Speed = 9 km/h

- Distance = Relative Speed x Time - Distance = 9 km/h x 2 hours - Distance = 18 km

Answer

The distance between the two cities is 8.88 km using Method 1 (calculating the average speed) and 18 km using Method 2 (calculating the relative speed).