Question

Из двух городов a и b в 15 00 навстречу друг другу выехали два поезда.Поезд,вышедший из A прибыл в B в 20-42,а поезд вышедший из b в a прибыл в a еще через 8 минут.определите,через сколько минут после отправления эти поезда встретились,если расстояние между A и B равно 285 км

Answer 1

20 ч 42 мин-15 ч=5 ч 42 мин   шел первый
5 ч 42 мин+8 мин=5 ч 50 мин  шел второй
5 ч 42 мин=5,7 ч
5 ч 50 мин=5 5/6 часа
285:5,7=50 (км/ч) скорость первого
285:5 5/6=285:35/6=342/7=48 6/7 (км/ч) скорость второго
50+48 6/7=98 6/7 (км/ч) скорость сближения
285:98 6/7=285:692/7=1995/692=2 611/692 (ч)
Ответ: они встретились через 2 611/692 часа после отправления

Answer 2

Problem Analysis

We are given that two trains, one starting from city A and the other from city B, depart towards each other at 15:00. The train from city A arrives at city B at 20:42, while the train from city B arrives at city A 8 minutes later. We need to determine how many minutes after their departure the trains meet, given that the distance between city A and city B is 285 km.

Solution

Let's break down the problem step by step:

1. Calculate the time it takes for the train from city A to travel from A to B. 2. Calculate the time it takes for the train from city B to travel from B to A. 3. Add the two times calculated in steps 1 and 2 to find the total time it takes for the trains to meet. 4. Convert the total time to minutes.

Step 1: Calculate the time for the train from city A to travel from A to B

To calculate the time it takes for the train from city A to travel from A to B, we need to subtract the departure time from the arrival time. The departure time is 15:00, and the arrival time is 20:42. Let's calculate the time difference:

Arrival time: 20:42 Departure time: 15:00

To calculate the time difference, we subtract the departure time from the arrival time:

20:42 - 15:00 = 5 hours and 42 minutes

So, the train from city A takes 5 hours and 42 minutes to travel from A to B.

Step 2: Calculate the time for the train from city B to travel from B to A

We are given that the train from city B arrives at city A 8 minutes after the train from city A arrives at city B. Therefore, the time it takes for the train from city B to travel from B to A is 8 minutes less than the time it takes for the train from city A to travel from A to B.

Time for the train from city B to travel from B to A = Time for the train from city A to travel from A to B - 8 minutes

Let's subtract 8 minutes from the time calculated in Step 1:

5 hours and 42 minutes - 8 minutes = 5 hours and 34 minutes

So, the train from city B takes 5 hours and 34 minutes to travel from B to A.

Step 3: Calculate the total time for the trains to meet

To calculate the total time it takes for the trains to meet, we need to add the time it takes for the train from city A to travel from A to B and the time it takes for the train from city B to travel from B to A.

Total time = Time for the train from city A to travel from A to B + Time for the train from city B to travel from B to A

Let's add the times calculated in Step 1 and Step 2:

5 hours and 42 minutes + 5 hours and 34 minutes = 11 hours and 16 minutes

So, the total time it takes for the trains to meet is 11 hours and 16 minutes.

Step 4: Convert the total time to minutes

To convert the total time to minutes, we need to multiply the number of hours by 60 and add the number of minutes.

Total time in minutes = (Number of hours * 60) + Number of minutes

Let's convert the total time calculated in Step 3 to minutes:

(11 hours * 60) + 16 minutes = 660 minutes + 16 minutes = 676 minutes

So, the trains meet after 676 minutes.

Answer

The trains meet after 676 minutes after their departure.

Note: The above solution assumes that the trains travel at a constant speed and there are no delays or stops along the way.