For a certain job, it takes 15 hours for Party A to do it alone, and 12 hours for Party B to do it alone. If Party A works alone for 1 hour, and Party B works alone for 4 hours, how many hours will it take for two people to work together on the rest? Use the equation of one variable to solve, thank you!

For a certain job, it takes 15 hours for Party A to do it alone, and 12 hours for Party B to do it alone. If Party A works alone for 1 hour, and Party B works alone for 4 hours, how many hours will it take for two people to work together on the rest? Use the equation of one variable to solve, thank you!

Suppose it takes x hours to finish
1-（1/15+4/12)=x(1/15+1/12) 3/5=3x/20 x=4

For a certain job, it takes 3 hours for Party A to work alone, and 4 hours for Party B to work alone. If Party A works alone for 1 hour and 50 minutes, and then they work together, how about cooperation
Set up equations and solve them

Let the cooperation time be x hours, then: 11 / 18 + (1 / 3 + 1 / 4) x = 1
（7/12）x=7/18
x=2/3

For a job, Party A and Party B work together for 4 hours, completing 25% of it, and then Party B work alone for 8 hours. At this time, the rest of the work will take 20 hours for Party A to complete. How many hours does it take for Party A to complete the work alone?

Solution 1: (1-25% - 25% × 2) / (20-8), = 14 / 12, = 148, 1 / 148 = 48 (hours); answer: it takes 48 hours for a to do the work alone. Solution 2: solve the equation with X hours for a and Y hours for B, then answer: it takes 48 hours for a to do the work alone