Question

Одна бригада может построить хранилище за 12 дней,вторая бригада за 9 дней.После того,как первая бригада проработала 5 дней,к ней присоединилась вторая и они вместе закончили работу. Сколько дней оаботали бригады вместе?

Answer 1

за 1 день первая бригада делает 1/12 часть работы а вторая 1/9. 
за первые пять дней было сделано 5/12 части работы и осталось 7/12(т.е. 21/36)
За один день две бригады делают 7/36 и для того чтобы сделать оставшиеся 21/36 работы и потребуется 3 дня

Answer 2

Problem Analysis

We are given that one team can build a storage facility in 12 days, while another team can build it in 9 days. After the first team works for 5 days, the second team joins them and they complete the work together. We need to determine how many days the teams worked together.

Solution

To solve this problem, we can calculate the work rate of each team and then use that information to find the total work done when they work together.

Let's assume that the work rate of the first team is x (in terms of the fraction of the storage facility built per day) and the work rate of the second team is y.

From the given information, we know that the first team can complete the work in 12 days, so their work rate is 1/12 of the storage facility per day. Similarly, the second team can complete the work in 9 days, so their work rate is 1/9 of the storage facility per day.

After the first team works for 5 days, they complete 5 * (1/12) = 5/12 of the storage facility. At this point, the second team joins them, and together they complete the remaining 1 - 5/12 = 7/12 of the storage facility.

Let's denote the number of days the teams work together as t. During this time, the combined work rate of the teams is x + y. We can set up the following equation to find t:

5/12 + t * (x + y) = 7/12

Simplifying the equation, we get:

t * (x + y) = 7/12 - 5/12 = 2/12 = 1/6

Now, we need to find the values of x and y. We know that the work rate of the first team is 1/12, so x = 1/12. Similarly, the work rate of the second team is 1/9, so y = 1/9.

Substituting these values into the equation, we have:

t * (1/12 + 1/9) = 1/6

Simplifying further, we get:

t * (3/36 + 4/36) = 1/6

Combining the fractions, we have:

t * (7/36) = 1/6

To solve for t, we can multiply both sides of the equation by 36/7:

t = (1/6) * (36/7) = 6/7

Therefore, the teams worked together for 6/7 of a day.

Answer

The first team worked for 5 days, and then the first and second teams worked together for 6/7 of a day. Therefore, the teams worked together for a total of 5 + 6/7 = 5 6/7 days.

Please let me know if you need any further clarification.