If the seventh grade students are allowed to do it alone, it will take 7.5 hours to complete. If the eighth grade students are allowed to do it alone, it will take five hours How much time does it take to finish the rest of the work if the seventh and eighth grade work together for one hour, and then the eighth grade finish the rest of the work alone? (solve the equation with one variable once)

If the seventh grade students are allowed to do it alone, it will take 7.5 hours to complete. If the eighth grade students are allowed to do it alone, it will take five hours How much time does it take to finish the rest of the work if the seventh and eighth grade work together for one hour, and then the eighth grade finish the rest of the work alone? (solve the equation with one variable once)

Single workload of grade one + single workload of grade two = total workload
Note: the total work quantity is 1
The results show that: 1
1/7.5+x/5=1
x/5=13/15
x=13/3

It takes 7.5 hours for a middle school to plant trees outside the school. It takes 5 hours for the eighth grade students to plant trees alone. Now let the seventh and eighth grade students plant trees together for one hour, and then let the eighth grade students complete the rest. How many hours do it take?

Suppose that it takes x hours to complete, from the meaning of the question, 17.5 + 15x = 1, the solution is: x = 413