A total of 697 trees were planted in grade 456. Half of the trees planted in grade 4 were equal to two fifths of those planted in Grade 5, and one third of the trees planted in grade 4 were equal to two seventh of those planted in Grade 6. How many trees were planted in grade 456?

Set up grade four and plant x trees
The number of trees in grade five = (x * 1 / 2) / (2 / 5) = 5 / 4 * x
The number of trees in Grade 6 = (x * 1 / 3) / (2 / 7) = 7 / 6x
Then: x + 5 / 4 * x + 7 / 6 * x = 697
The solution is x = 204
The number of trees in Grade 5 = (x * 1 / 2) / (2 / 5) = 5 / 4 * x = 255
The number of trees in Grade 6 = (x * 1 / 3) / (2 / 7) = 7 / 6x = 238

There are 800 students in a primary school. Half of the students in the lower grade are equal to two fifths of the students in the middle grade, and one fourth of the students in the lower grade are equal to the students in the higher grade
One in seven. How many people are there in junior, middle and senior grades?

The number of students in lower grades: the number of students in middle grades = 2 / 5:1 / 2 = 4:5
Number of junior students: number of senior students = 1 / 7:1 / 4 = 4:7
Therefore, the number of lower grade students: the number of middle grade students: the number of higher grade students = 4:5:7
The number of students per class is: 800 (4 + 5 + 7) = 50 (people)
Junior students: 50 × 4 = 200
Middle grade students: 50 × 5 = 250
Senior students: 50 × 7 = 350

There are 615 students in grade 4, 5 and 6. Half of the students in Grade 6 are equal to 2 / 5 of the students in Grade 5 and 3 / 7 of the students in grade 4,
It's better to have both equations and formulas

My friends upstairs, where is the ternary equation (three unknowns) from the primary school? It can be seen that my friends are not clear about this problem. I am a primary school teacher,
Think: set the fourth grade as X person
"1 / 2 of the sixth grade equals 2 / 5 of the fifth grade equals 3 / 7 of the fourth grade"
Two fifths of the fifth graders are equal to three fifths of the fourth graders
1 / 2 of the sixth grade is equal to 3 / 7: 3 / 7 x △ 1 / 2 of the fourth grade
There are 615 students in grade 4, 5 and 6: x + 3 / 7 x △ 2 / 5 + 3 / 7 x △ 1 / 2 = 615
Sorting calculation: x = 210 fourth grade
Grade 5: 3 / 7 × 210 △ 2 / 5 = 225
Grade 6: 3 / 7 × 210 △ 1 / 2 = 180

There are 720 students in 456 grade. How many students are there in three grades?
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Suppose there are X students in Grade 5, then the students in grade 4 are 1.5x, and the students in Grade 6 are 2x. There are x + 1.5x + 2x = 720 students in total. The solution is x = 160, 1.5x = 240, 2x = 320

There are 615 students in grade 4, 5 and 6 of Yuying primary school. It is known that 12 students in Grade 6 are equal to 25 students in Grade 5 and 37 students in grade 4. How many students are there in each of these three grades?

Suppose there are X students in Grade 6, then there are 12x ／ 25 students in Grade 5, 12x ／ 37 students in grade 4, 12x ／ 37 + 12x ／ 25 + x = 615, 76x + 54x + x = 615, 76x + 54x + x = 411

There are 280 students in grade 4 and grade 5,
There are 322 students in total. The number of students in the fifth grade accounts for two fifths of the total number of students in the three grades,

280 + 322 = 602 (person)
It's the total number of students in three grades
1＋2/5＝7/5
There are three grades
602 △ 7 / 5 = 430 (person)
There are many students in grade five
430 × 2 / 5 = 172 (person)

There are 120 students in the fifth grade and 160 students in the sixth grade of a primary school. The sum of the number of students in the fifth and sixth grade is just 35% of the total number of students in the whole school
2. To build a highway, one fourth of its total length was built for the first time, and 15% for the second time. At this time, it is 6 kilometers away from the midpoint of the highway. How long is the highway?

（120+160）/35%=280*20/7=800
6/（1-25%-15%）=10

How many hours is 1:15

One and a quarter of an hour

How many hours is 72 minutes in fractions

6 / 5 hours

How many hours is 24 minutes equal to

24 minutes is equal to 0.4 hours, and then expressed as 2 / 5 hours in fractions

A total of 697 trees were planted in grade 456. Half of the trees planted in grade 4 were equal to two fifths of those planted in Grade 5, and one third of the trees planted in grade 4 were equal to two seventh of those planted in Grade 6. How many trees were planted in grade 456?