Question

Первая снегоуборочная машина может убрать улицу за 2ч, а вторая - за 60% этого времени. вторая машина приступила к работе спустя некоторое время после того, как начала работать первая. Затем они вместе закончили работу за 30 минут. На сколько минут позже первой машины вторая машина приступила к работе?

Answer 1

30 мин=1/2 ч=0,5 ч
Всю работу примем за 1, тогда 1/2 или 0,5 части улицы в час скорость уборки первой машины.
1/2*60:100=0,3 части улицы может убрать вторая машина за 1 час.
0,3+0,5=0,8 части улицы могут убрать за 1 час обе машины
0,8*0,5=0,4 части улицы убирали за 30 минут, работая вдвоем
1-0,4=0,6 части улицы убирала первая машина
0,6:0,5=1,2 ч  работала первая машина одна
1,2*60=72 минуты
Ответ на 72 минуты позже первой машины вторая машина приступила к работе

Answer 2

Problem Analysis

We are given two snow removal machines, where the first machine can clear a street in 2 hours, and the second machine can clear 60% of that time. The second machine starts working after some time has passed since the first machine started. Together, they finish the job in 30 minutes. We need to determine how many minutes after the first machine started the second machine began working.

Solution

Let's assume that the first machine started working at time t=0. We need to find the time at which the second machine started working.

Let's calculate the time it takes for the first machine to complete the job: - The first machine can clear the street in 2 hours, which is equivalent to 120 minutes.

Now, let's calculate the time it takes for the second machine to complete the job: - The second machine can clear 60% of the time it takes for the first machine to complete the job. - Therefore, the second machine can clear the street in 0.6 * 120 minutes = 72 minutes.

Next, let's determine the time it takes for both machines to complete the job together: - Together, they finish the job in 30 minutes.

To find the time at which the second machine started working, we can subtract the time it takes for both machines to complete the job from the time it takes for the first machine to complete the job: - Time at which the second machine started working = Time taken by the first machine - Time taken by both machines together - Time at which the second machine started working = 120 minutes - 30 minutes = 90 minutes.

Therefore, the second machine started working 90 minutes after the first machine started.

Answer

The second machine started working 90 minutes after the first machine started.