Practical problems, urgent solution to explain the idea of solving the problem

There are x boys in the mathematics interest group, and there are y people in the mathematics interest group.

According to the conditions given in the question, you can list 1 system of binary equations:

4y/7=x ①

5/8(y+6)=x+6 ②

Then just solve this system of equations.

I calculated that it was x=24, which means that there were 24 boys in the math interest group.

If there's anything I don't understand, you can tell me

Analysis: Use the volume rate to answer the fraction, and the percentage application problem must pay attention to whether the amount of unit 1 changes before and after; If unit 1 remains the same, it can be used: specific quantity The fraction corresponding to the specific quantity = the quantity of unit 1.

For example, unit 1 in this problem is the number of people in the interest group, and its amount changes before and after, so it must be converted into unit 1; When converting, you can use the same amount before and after as a unit.

The number of female students in this question remains the same, and the number of female students is used as a unit of 1

It turned out that the number of boys accounted for 4 7 of the group size, that is, the number of boys was 4 3 of the number of girls

Now the number of boys is 5 8 of the group size, i.e. the number of boys is 5 3 of the number of girls

Corresponding to the volume rate: The number of male students increased The number of male students increased = the amount of unit 1 (i.e., the number of female students) 6 (5 3-4 3) = 18 (the number of female students) The number of male students = the number of female students 5 3

18 5 3 = 30 people.

It turns out that there are x boys and y girls.

x/x+y=4/7

x+6/x+y+6=5/8

x=24y=18

So now there are 24 + 6 = 30 boys.

Roll a square sheet of paper with a side length of 50 cm into a cylinder as large as possible.

1) What is its underside circumference? (

Its underside circumference = side length of the square = 50 cm.

2) What is its height? (

Its height = the length of the sides of the square = 50 cm.

3) What is its side area? (

Its side area = the area of the square = 50 50 = 2500 square centimeters.

Hello, when you consider the problem of rolling a square paper with a side length of 50 cm into a cylinder as large as possible, when the two sides of the square paper are connected end to end, the cylinder that appears is the largest.

1) At this time, the circumference of the bottom surface of the cylinder is one side of the square, so the circumference of the bottom surface of the cylinder is 50cm.

2) The height of the circle is 50cm on the side of the square. (3) The formula for the side area is the circumference of the bottom surface multiplied by the height, so the side area of 50x50 is equal to 2500 square centimeters.

(1) The circumference is 50cm, according to a side roll, roll a circle, then the bottom edge of the circumference is just the side length of the square.

2) The height is 50cm

3) The side area is 50 50 = 2500 square centimeters.

3.(1).Its base circumference is 50cm;

2).Its height is 50cm;

3).Its side area is:

50*50=2500（cm^2）。

According to the question, it can be concluded that:

1. Bottom circumference: 50cm

2. Height: 50cm

3. The side area s=2 rh=2 x 25 x 50=2500 square centimeters The radius is through the bottom perimeter c = 2 r = 50

This gives r=25

(1), bottom circumference: 50cm

2. Height: 50cm

Measured area: 50x50=2500cm2

(1) The circumference of the bottom surface is 50

2) The height is also 50

3) Base area multiplied by height.

Let Xiao Li run 5x kilometers per hour and Xiao Zhang run 4x kilometers per hour.

5x*2+4x*2=36, the solution is x=2, so Xiao Li runs 10 kilometers per hour.

5+4=9

36 5 9 2 = 10 (km).

A: Xiao Li runs 10 kilometers per hour.

Ask for A and B to be x and y years old.

x+y=98

y-（x-y/2）=x

Solution: x=42

y=56

The answer is A: years old, B: years old. Thank you.

See if there's anything wrong with the question?

[Answer].

Solution: If there are x singles matches, then there are (68-x) doubles matches, and 2x+4 (68-x)=208 is obtained according to the equation of the question

2x+272-4x=208

64=2xx=32

A: There are 32 singles and 36 doubles.

Set a bag of apples for x dollars. You can know that Xiao Ming brought x-5 yuan. Xiaojie brought x-3 yuan.

Can be listed as (x-5) + (x-3) = x+8

x gets 16 so a bag of apples is 16 yuan, but the question is how much is per kilogram, a bag is 5 kilograms, so divide 16 by 5 is 1 kilogram of money, that is.

Solution: Xiao Ming has x yuan, Xiao Jie has y yuan.

x+5=y+3

x+y-8=x+5

x=11y=13

x+5=16 (yuan) 16 5=yuan kilograms).

Set up a big monk x people, a small monk y people. Then there is a system of binary linear equations 3x+y 3=100

x+y=100

The solution is x=25 y=75

Set up a big monk x a small monk y

x+y=100

Three large steamed buns.

A small steamed bun.

3x + y of 3 = 100

x+y=100

9x+y=300

8x+y=200

x=25 substitution

25+y=100

y=75 check the monk 25x3=75.

Small monk 75x1/3 = 25.

Big 25 Small 75

Solution: If A's deposit is $x, then B's deposit is $108-x.

1-2/5)x=108-x-12

x=60108-x=108-60=48 yuan.

Answer: A's original deposit was 60 yuan, and B's original deposit was 48 yuan.

Analysis: If A withdraws two-fifths of his deposit and B withdraws 12 yuan, then the amount of money saved by the two is equal, and it can be obtained: after B withdraws 12 yuan, the rest is A's deposit (1 two-fifths three-fifths) 3 5, then A and B have deposited a total of 108 yuan, which can be understood in this way:

108 12 96 yuan First of all, the deposit of A is regarded as unit one, and this 96 yuan is the deposit of A plus the remaining deposit of B (the remaining deposit of B is three-fifths of the deposit of A), that is: 96 yuan is the deposit of A 3 5 of the deposit of A = 1 and 3 5 of the deposit of A Then the original deposit of A is calculated as: 96 1 and 3 5 60 yuan.

B deposits: 108 60 58 yuan.

Comprehensive formula: A deposit: (108 12) (1 1 two-fifths) 60 (yuan) B deposit: 108 60 58 (yuan).

A: ——