For a section of highway, the original plan was that team a and team B would build it together in 20 days. In fact, team a would build it 12 days first, then team B would join team a for 13 days, and team B would build the rest in 3 days. How many days would it take for team a and team B to build this section of highway separately?

For a section of highway, the original plan was that team a and team B would build it together in 20 days. In fact, team a would build it 12 days first, then team B would join team a for 13 days, and team B would build the rest in 3 days. How many days would it take for team a and team B to build this section of highway separately?

A's work efficiency: (1 − 120 × 16) / (12-3) = (1-45) / (9 = 15 × 19 = 145); B's work efficiency: 120 − 1459180 − 4180 = 5180 = 136; 1 − 145 = 45 (days); 1 − 136 = 36 (days); a: it takes 45 days for team a to complete this section of road alone, and 36 days for team B to complete this section of road alone

Team a and team B planned to build a section of highway in 20 days. Team a built it 12 days before team B joined the team
Suppose the equation

I did the problem by looking at the problem upstairs
If the efficiency of a is x, the efficiency of B is 1-x of 20
20 × [x + (1 / 20-x)] = 12x + 13X + 13 (1 / 20-x) + 3 (1 / 20-x)
20x + 1-20x = 25X + 13-13x of 20 + 3-3x of 20
1 = 12x + 16 / 20-3x
1 = 9x + 16 / 20
9x = 4 / 20
X = 4 out of 180. It's work efficiency. If you want to calculate time, you should use 1 △ work efficiency
It takes 45 days for Party A to build this section of road separately. For Party B to build this section of road separately, first use 1 / 20-4 / 180 = 5 / 180, and then use 1 / 180 5 = 36 days

To build a highway, Party A will finish it in 15 days, Party B will finish it in 20 days, Party A will leave several days later, and the remaining highways will be finished in 8 days. How many days will party a finish it?

B repaired for 20 days alone, and actually repaired for 8 days. A total of 8 / 20 = 40% was repaired. It can be seen that a was repaired for 60%, so a was repaired for 15 * 60% = 9 days

Team a and team B built a road together. When they finished the task, team a built 815% of the road. If team B finished it alone in 24 days, how many days did team a finish it alone? (Qingshan District, Wuhan City)

The working time of team a and team B: (1-815) △ 124, = 715 × 24, = 565 (days); team a does it alone for several days: 1 △ 815 △ 565, = 1 △ 121, = 21 (days). Answer: team a does it alone for 21 days