There is a batch of books that Xiaoliang can bind in 9 days and Xiaodong can bind in 20 days. How many days can Xiaoliang and Xiaodong cooperate to finish this batch of books?

There is a batch of books that Xiaoliang can bind in 9 days and Xiaodong can bind in 20 days. How many days can Xiaoliang and Xiaodong cooperate to finish this batch of books?

1 / (1 / 9 + 1 / 20) = 6.21 days
It will be finished in seven days

There is a batch of books. Xiaoming can bind three fourths of the books in nine days, Xiaoli can bind five sixths of the books in twelve days, and they can finish two thirds of the books in a few days

2/3÷(3/4÷9+5/6÷12)
=2/3÷(1/12+5/72)
=2/3÷11/72
=48 / 11 days
In 48 / 11 days, two-thirds of the books can be completed

Xiao Ming's books are twice as many as Xiao Fang's. Xiao Ming gave Xiao Fang three books, and they have the same number of books. How many of them have solved equations

If Xiao Fang has x books, Xiao Ming has 2x
2x-3=x+3
x=6
2x=2x6=12
So Xiao Fang has 6 books and Xiao Ming has 12 books