There are a total of 90 students in the two classes of the sixth grade of Tianshan Primary School.

After the transfer of 4 people from Class A to Class B.

4:5 The total number of people remains unchanged at 90

It shows that at this time, there are 40 people in A and 50 people in B.

Then it turns out that A 40 + 4 = 44 people.

Divide 44 by 2/35 to get the original 770 for the whole school

There is X in Class A and Y in Class B

Then x+y=90, (x-4) (y+4)=4 5, and the simultaneous solution is x=44, and the original class A accounts for 2/35 of the whole school, and the whole school is 44 (2 35)=770 people.

Set up: Class A x people.

x-4):(90-x+4)=4:5

Get x=44

So 44 students in class A and 46 students in class B, the whole school = 44 2 * 35 = 770 people.

If there are x people in class A, then there will be 90 x people in class B.

x-4）:（90-x+4）=4:5

X 44 so there are 44 people in class A and 46 people in class B.

"Whole school" is the unit "1", because it is unknown, and the unit one is unknown, so division is used.

So there are 770 people in the whole school.

Class A x people and B class y people.

x+y=90

x-4）/（y+4）=4/5

Solution: y=46 x=44 Total number of students=x (2 35), so the whole school has 770 students.

There are a total of 90 students in the two classes of the sixth grade, and 4 students from class A are transferred to class B, and the ratio of class A to class B is 4:5

So, later the number of people was 40 in class A and 50 in class B.

Originally, the number of students in Class A was 44, and the number of students in the whole school was 44 [2 35]=770.

Because 4:5

So after A: 40 B: 50

Originally: A 44 B 46

The whole school has 44 35 2 770 students.

There are x people in class A.

x-4):(90-x+4)=4:5

x=44 There are y people in the whole school.

44/y=2/35

y=770

Class 1: 87x15 29=45 (person).

Second shift: 87x14 29=42 (human mold skin).

Answer: (slightly gripped).

Hope it can help you!

There are 6 more people in Class 1 and 9 people in Class 3.

is equal to 2 classes.

So the second class (138+6+9) 3=51 people.

51-6 = 45 people per class.

3 shifts 51-9 = 42 people.

Solution: If there are x people in the first class, there will be (x+6) people in the second class, and (x+6-9) people in the third class.

x+(x+6)+(x+6-9)=138

3x+3=138

3x=135

x=45 then there are 45+6=51 (people) in the second shift, and 51-9=42 (people) in the third shift.

960 12 80 (person) Answer: On average, there are 80 students per class.