The students in the three groups of a, B and C went to plant trees. The average number of trees planted in the two groups was 18. The average number of trees planted in the two groups was 17. The average number of trees planted in the two groups was 19 I want to know how to solve the formula with the method of grade 5 in primary school

The students in the three groups of a, B and C went to plant trees. The average number of trees planted in the two groups was 18. The average number of trees planted in the two groups was 17. The average number of trees planted in the two groups was 19 I want to know how to solve the formula with the method of grade 5 in primary school

Because each group uses it twice
So three small combinations of a, B and C can be planted
(18 + 19 + 17) divided by 2 = 27
A + B = 18, so C is 9
Similarly, a is 8, B is 10

The students of group A, B, C and D planted 45 trees. If group a planted 2 more trees, group B planted 2 less trees, group C planted 2 times more trees, and group D planted half less trees, then the trees planted in the four groups were exactly the same. How many trees did the four groups plant?
It's better to use the line diagram instead of the equation. It's better to use the formula and the solution,

The dash is a little hard to look like, so I dictate it here. You can mark it in the book as I say
First of all, we should start from the trees in which they all planted the same tree. Therefore, we can draw four lines of the same length, and add or subtract the length of the line appropriately according to their relationship. Therefore, the same length is obtained by adding 2 trees to the original number of a, and the same length is obtained by subtracting 2 trees from the original number of B (adding 2 trees to the same length), The original number of C multiplied by 2 is the same length (so C is half of the same length). The original number of D divided by 2 is the same length (D is twice the same length). These four numbers are exactly the same, and their relationship is the same. Therefore, let's suppose that their same number is x, then the actual number of a is X-2, B is x + 2, C is x / 2, D is 2x, so the sum of them is 45. All of them add up to a linear equation of one variable, and finally x = 10, so a, B, C and D are 8, 12, 5 and 20 respectively
I hope you can understand what I said,
Digression, a lot of people say I can't express things clearly, so let's verify it from you, hope to help you

40 students from Class 3 (1) participated in tree planting. Each boy planted 3 trees and each girl planted 2 trees. It is known that there are 30 more trees for boys than for girls. How many are there for boys and girls?

Suppose there are x boys, then there are (40-x) girls. According to the meaning of the title, we get 3x - (40-x) × 2 = 30, & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; 3x-80 + 2x = 30, & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; 5x = 110, & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; X = 22, 40-x = 40-22 = 18. A: there are 22 boys and 18 girls

We went to plant trees. A total of 123 trees were planted. It is known that the trees planted by the teacher are the same as those of each student. How many students are there in this class and how many trees are planted by each student

123=3×41
So there are 41 - 1 = 40 students in this class, and each student plants 3 trees