1. For a project, team a will do it alone for 15 days, team B will do it alone for 20 days, team a will do it alone for 5 days, and team a and team B will do it together for several days. A total of 4 / 5 of the whole project will be completed? 2. The task of processing a batch of parts directly from one car is completed by the first group in 20 days, and by the second group in 30 days. Now, it is done by the second group for 6 days, and then by the combination of one and two for 3 days. The rest is completed by the first group. How many days will it take? 3. For a pond, it takes 20 hours to operate a single pump, 30 hours to operate B single pump, and 15 hours to operate C single pump?

1. For a project, team a will do it alone for 15 days, team B will do it alone for 20 days, team a will do it alone for 5 days, and team a and team B will do it together for several days. A total of 4 / 5 of the whole project will be completed? 2. The task of processing a batch of parts directly from one car is completed by the first group in 20 days, and by the second group in 30 days. Now, it is done by the second group for 6 days, and then by the combination of one and two for 3 days. The rest is completed by the first group. How many days will it take? 3. For a pond, it takes 20 hours to operate a single pump, 30 hours to operate B single pump, and 15 hours to operate C single pump?

1. A project is completed by team a alone for 15 days, team B alone for 20 days, team a alone for 5 days, and then team a and team B work together for several days. A total of 4 / 5 of the whole project is completed, and then team a and team B work together for X days 5 * 1 / 15 + X * (1 / 15 + 1 / 20) = 4 / 5x = 42