It takes 8 days for Party A and 10 days for Party B to complete a single project. Now, two people work together. Party A has a day off due to illness. How many days does it take to complete the project?

It takes 8 days for Party A and 10 days for Party B to complete a single project. Now, two people work together. Party A has a day off due to illness. How many days does it take to complete the project?

In the middle of a day off because of illness, can be seen as a day for B alone, the remaining two cooperation
A completes 1 / 8 in one day, B completes 1 / 10 in one day
（1-1/10）/（1/8+1/10）
=（9/10）/（9/40）
=4 days
4 + 1 = 5 days
A: it takes five days to complete the project

1. Class A, class B and class C do good deeds. The number of good deeds done by class A is half that of class B. the number of good deeds done by class C is three times that of class B. class C does 75 more good deeds than Class A. how many good deeds does class a do?
2. There are 60 peach trees and pear trees. The number of peach trees is seven eighths of that of pear trees. How many peach trees are there
(1) After finding out the answer, fill in: how many peach trees account for the total number of peach trees and pear trees?
(2) Can you solve the equation?
Completion
1. The ratio of number a to number B is 4:5, and number B is ()% more than number a
2. The number of clothes sold accounts for three-quarters of those not sold, and the number of clothes sold accounts for () copies. The total number of clothes sold is divided into () copies, and the number of clothes not sold accounts for () copies

(1) If class A does x good deeds, class B does 2x good deeds, and class C does 6x good deeds. According to the meaning of the question, 6x-x = 75, so x = 15
(2) Method 1
If the number of peach trees is 7 / 8 of that of pear trees, the sum of the two trees is 7 / 8 + 1 of that of pear trees. There are 60 pear trees in total
60 (7 / 8 + 1) = 32 (trees), 60 - 32 = 28 (trees) of peach trees
Method 2
If the number of peach trees is 7 / 8 of the number of pear trees, the total number of trees can be divided into (7 + 8) = 15, and the number of peach trees accounts for 7 of them, so the number of peach trees is 60 × 7 / 15 = 28
The number of peach trees accounted for 7 / 15 of the total;
Method 3
Suppose there are x pear trees, then there are 7x / 8 peach trees, that is, x + 7x / 8 = 60, the solution is: x = 32 (trees), 60-32 = 28 (trees)
Fill in the blanks:
(1) Number B is 25% more than number a
(2) The number of clothes sold accounted for three-quarters of those not sold, three sold and four not sold. The total number of clothes was divided into seven on average, and three out of seven were not sold
Supplementary question:
(1) The number a is 4 / 7 of the sum of a and B
(2) Boys account for 4 / 3 of girls, boys account for 4, girls account for 3. Boys account for 4 / 7 of the class, girls account for 3 / 7 of the class

A sixth grade Olympiad math problem, speed
For a project, it takes 20 days for team a to do it alone, and 30 days for team B to do it alone. After several days for team a to do it alone, team B will continue to do it. It takes 29 days to complete the task. How many days did team a do it? How many days did Team B do it?

Let a do it alone for X days, and B do it for 29-x days
1/20×x+1/30×(29-x)=1
1/20x+29/30-1/30x=1
1/20x-1/30x=1-29/30
1/60x=1/30
x=2
B: 29-2 = 27 days

A and B walk towards each other at the same time from a and B, and meet on the way 2 hours later. After meeting, the walking speed of a and B increases by 1 km / h. When a arrives at B, they immediately return to a, and when B arrives at a, they immediately return to B, and they meet again 3 hours and 36 minutes after the first meeting. What is the distance between a and B?